Method of determining viscosity by exciting two measuring tubes using two actuators

ABSTRACT

A method for determining the viscosity of a medium with a Coriolis mass flowmeter having at last two measuring tubes through which a medium can flow, comprising: exciting the measuring tubes; and determining at least the viscosity of the medium by evaluation of measured values obtained from the measuring device. The measuring values comprise the amplitude of torsional oscillation reached, wherein the amplitude of torsional oscillation reached is evaluated for determining the viscosity of the medium at a set excitation intensity of the measuring device and using the damping coefficient of the medium.

CROSS-REFERENCE TO RELATED APPLICATION

This is a Continuation of U.S. patent application Ser. No. 12/659,535,which was filed on Mar. 11, 2010, and will issue as U.S. Pat. No.8,316,722 on Nov. 27, 2012; and is a Nonprovisional Application claimingthe benefit of U.S. Provisional Application No. 61/202,543, filed onMar. 11, 2009, and U.S. Provisional Application 61/213,742, filed onJul. 9, 2009.

TECHNICAL FIELD

The invention relates to a measuring system for measuring a viscosityand/or a Reynolds number of a medium flowing in a pipeline, especiallyan aqueous liquid, a slurry, a paste, or other flowing material. Themeasuring system includes a measuring transducer of vibration-type, aswell as a transmitter electronics connected thereto.

BACKGROUND DISCUSSION

In the field of process measurements and automation technology, formeasuring physical parameters, such as e.g. the mass flow, densityand/or viscosity of media flowing in pipelines, often such measuringsystems formed as inline measuring devices of compact construction areused, which, by means of a measuring transducer of vibration-typethrough which the medium flows, and a transmitter electronics connectedthereto, effect reaction forces in the medium, such as e.g. Coriolisforces corresponding with the mass flow, inertial forces correspondingwith the density of the medium, and/or frictional forces correspondingwith the viscosity of the medium, and, derived from these, produce ameasurement signal representing the respective mass flow, density and/orviscosity of the medium. Such measuring transducers, in part embodiedalso as multivariable Coriolis mass flow/viscosity meters or Coriolismass flow/density/viscometer, are described in detail in e.g. EP-A 1 001254, EP-A 553 939, U.S. Pat. No. 4,793,191, US-A 2002/0157479, US-A2006/0150750, US-A 2007/0151368, US-A 2010/0050783, U.S. Pat. No.5,370,002, U.S. Pat. No. 5,602,345, U.S. Pat. No. 5,796,011, U.S. Pat.No. 6,308,580, U.S. Pat. No. 6,415,668, U.S. Pat. No. 6,711,958, U.S.Pat. No. 6,920,798, U.S. Pat. No. 7,134,347, U.S. Pat. No. 7,392,709,WO-A 96/08697, WO-A 03/027616, WO-A 2008/059262, WO-A 2009/120222 orWO-A 2009/120223.

Each of the measuring transducers includes a transducer housing, whichis formed from an inlet-side, first housing end, at least partially bymeans of two or four, first flow divider, having in each case circularlycylindrical or conical flow openings spaced apart from one another, andfrom an outlet-side, second housing end formed at least partially bymeans of two or four, second flow divider, having in each case flowopenings spaced apart from one another. In the case of at least some ofthe measuring transducers illustrated in U.S. Pat. No. 5,602,345, U.S.Pat. No. 5,796,011, U.S. Pat. No. 7,350,421, or US-A 2007/0151368, thetransducer housing comprises a rather thick walled, circularlycylindrical tube segment, which forms at least a middle segment of thetransducer housing.

For conveying the at least sometimes flowing medium, the measuringtransducers comprise furthermore, in each case, at least two measuringtubes connected for parallel flow—in each case straight, or in each caseequally curved—made of metal, especially steel or titanium, which tubesare placed within the transducer housing, and are oscillatably heldtherein by means of the aforementioned flow dividers. A first of theequally constructed measuring tubes, extending parallel to the other,opens into a first flow opening of the inlet-side, first flow dividerwith an inlet-side, first measuring tube end, and into a first flowopening of the outlet-side, second flow divider with an outlet-side,second measuring tube end. A second of the measuring tubes opens into ina second flow opening of the first flow divider with an inlet-side,first measuring tube end, and into a second flow opening of the secondflow divider with an outlet-side, second measuring tube end. Each of theflow dividers includes additionally, in each case, a flange with asealing surface for the fluid-tight connecting of the measuringtransducer to pipe segments of the pipeline serving to supply the mediumto, or to carry the medium away from, the measuring transducer.

The measuring tubes of known measuring systems of the aforementionedtype are caused to vibrate during operation for the purpose of producingthe aforementioned reaction forces, driven in the so-called driven, orwanted, mode by an exciter mechanism serving to produce or maintainmechanical oscillations of the measuring tubes—in this case, bendingoscillations about an imaginary oscillation axis, which imaginarilyconnects the respective first and second measuring tube ends. Theoscillations in the wanted mode are, particularly also in applicationsof the measuring transducer in measuring systems formed as Coriolis massflow- and/or density measuring devices, developed as lateral bendingoscillations, and bear superimposed thereon, in the case of mediumflowing through the measuring tubes, as a result of Coriolis forcesinduced therein, additional, equal frequency oscillations in theso-called Coriolis mode. Accordingly, the exciter mechanism—here mostoften electrodynamic—in the case of straight measuring tubes, isembodied in such a manner that the two measuring tubes in the wantedmode at least partially—most often, however, predominantly—can beexcited differentially to opposite phase bending oscillations in ashared plane of oscillation; that is, by entry of exciter forcessimultaneously along a shared line of action, however, acting inopposite directions by means of at least one oscillation exciter linkedjust to the two measuring tubes. As, among other things, evident fromthe mentioned US-A 2006/0150750, based on opposite phase bendingoscillations of two measuring tubes, besides mass flow and density, theviscosity of the medium conveyed in the measuring transducer can also beascertained, for instance, based on an electrical excitation power, fedfrom the transmitter electronics to the exciter mechanism, serving toovercome the damping of the measuring tube oscillations caused alsoparticularly by the medium located in the measuring tubes.

For registering of vibrations, especially of oscillations of themeasuring tubes excited by the exciter mechanism, and for producingoscillation measurement signals serving as vibration representing,primary signals of the measuring transducer, the measuring transducershave additionally, in each case, a sensor arrangement, most oftenlikewise electrodynamic, which reacts to relative movements of themeasuring tubes. Typically, the sensor arrangement is formed by means ofan inlet-side oscillation sensor, registering oscillations of themeasuring tubes differentially—thus only relative movements of themeasuring tubes as well as of an outlet-side oscillation sensor, alsoregistering oscillations of the measuring tubes differentially. Each ofthe normally equally constructed oscillation sensors is formed by meansof a permanent magnet held on the first measuring tube, and acylindrical coil, permeated by the magnetic field of the permanentmagnet, held on the second measuring tube.

In operation, the above described tube arrangement, formed by means ofthe at least two measuring tubes, with the, in each case shared holdingof the exciter mechanism and the sensor arrangement of the measuringtransducer, is excited by means of the electromechanical excitermechanism, at least at times, in the wanted mode, to execute mechanicaloscillations at at least one, dominating, wanted oscillation frequency.As oscillation frequency for the oscillations in the wanted mode, insuch case, usually an instantaneous natural eigen, or resonance,frequency of the tube arrangement is selected, which frequency, in turn,is essentially dependent on the size, shape and material of themeasuring tubes as well as on an instantaneous density of the medium. Asa result of the fluctuating density of the medium to be measured, and/oras a result of performing a change of media during operation, the wantedoscillation frequency is variable during operation of the measuringtransducer naturally at least within a calibrated and, insofar,predetermined, wanted frequency band, which correspondingly has apredetermined lower and a predetermined upper limit frequency.

For defining a free oscillatory length of the measuring tubes, andassociated therewith, for adjusting the wanted frequency band, measuringtransducers of the above described type comprise additionally most oftenat least one inlet-side coupling element for forming inlet-sideoscillation nodes for opposite phase vibrations, especially bendingoscillations, of both measuring tubes, which element is affixed to bothmeasuring tubes spaced apart from both flow dividers, as well as atleast one outlet-side coupling element for the forming of outlet-sideoscillation nodes for opposite phase vibrations, especially bendingoscillations of the measuring tubes, which element is affixed to bothmeasuring tubes, spaced apart from both flow dividers as well as fromthe inlet-side coupling element. In the case of straight measuringtubes, a minimum distance between inlet side and outlet side couplingelements—insofar as they belong to the tube arrangement—corresponds to,in such case, the free oscillatory length of the measuring tubes. Bymeans of the coupling elements, additionally an oscillation qualityfactor of the tube arrangement, such as the sensitivity of the measuringtransducer, can also be, on the whole, influenced in such a manner that,for a minimum required sensitivity of the measuring transducer, at leastone minimum free oscillatory length is to be provided.

Development in the field of measuring transducers of vibration-type inthe meantime has reached a state such that modern measuring transducersof the described type can, for practical purposes, satisfy highestrequirements with respect to precision and reproducibility of themeasurement results for a broad application spectrum in the field offlow measurement technology. As a result, such measuring transducers areused in practice for applications with mass flow rates from only a fewg/h (grams per hour) up to some t/min (tons per minute), at pressures ofup to 100 bar for liquids or even over 300 bar for gases. Due to thehigh bandwidth of their opportunities for use, industrial grademeasuring transducers of vibration-type are available with nominaldiameters (corresponding to the caliber of the pipeline to be connectedto the measuring transducer, or to the caliber of the measuringtransducer measured at the connecting flange), which lie in a nominaldiameter range between 1 mm and 250 mm, and are specified for maximumnominal mass flow rate 2200 t/h, respectively, for pressure losses ofless than 1 bar. A caliber of the measuring tubes lies, in such case,for instance, in a region between 80 mm and 100 mm.

As already mentioned, with measuring systems having measuring tubesexecuting bending oscillations, the viscosity, or also measuredvariables dependent upon it, such as, for instance, the Reynolds number,can also be ascertained, measurable based on the viscosity, and, indeed,also with bending oscillations (see also US-A 2006/0150750) However, inthe case of this method, particularly also as a result of the often verysmall amplitude of the wanted oscillations, the sensitivity of themeasuring transducer can have a certain dependency on the nominaldiameter, and, indeed, in such a manner that the sensitivity decreaseswith the increasing nominal diameter. As a result, also the accuracy ofmeasurement can become less with the increasing nominal diameter, or therespective transmitter electronics is presented with increasedrequirements with regard to signal processing technology and computingpower. In spite of this, in the meantime, measuring transducers are alsoavailable for the purposes of measuring viscosity for use in pipelineswith very high mass flow rates, and associated therewith, very largecalibers of over 50 mm; there is quite a significant interest inmeasuring transducers of high precision and low pressure loss also forviscosity measurements in the case of still greater pipeline calibers,for instance, 100 mm or more, or mass flow rates of 1200 t/h or more, tobe used, for instance, for applications in the petrochemical industry,or in the area of transporting and handling petroleum, natural gas,fuels, etc. This leads, in the case of a correspondingly scaledenlargement of already established measuring transducer concepts knownfrom the state of the art, especially as set forth in EP-A 1 001 25₄,EP-A 553 939, U.S. Pat. No. 4,793,191, US-A 2002/0157479, US-A2007/0151368, U.S. Pat. No. 5,370,002, U.S. Pat. No. 5,796,011, U.S.Pat. No. 6,308,580, U.S. Pat. No. 6,711,958, U.S. Pat. No. 7,134,347,U.S. Pat. No. 7,350,421, or WO-A 03/027616, to the fact that thegeometric dimensions—especially the installed length corresponding to adistance between the sealing surfaces of both flanges, and in the caseof curved measuring tubes, to a maximum lateral expansion of themeasuring transducer—especially as resulting from the desiredoscillation characteristics, the required loading capacity, as well asthe maximum allowed pressure loss, would become very large. Associatedtherewith, also the empty mass of the measuring transducer unavoidablyincreases, with conventional measuring transducers of large nominaldiameters already implemented having an empty mass of, for instance, 400kg. For measuring transducers with two bent measuring tubes, forinstance, according to U.S. Pat. No. 7,350,421 or U.S. Pat. No.5,796,011, investigations have been performed concerning their scalingto still greater nominal diameters. These investigations have shown, forexample, that for nominal diameters of more than 300 mm, the empty massof a conventional measuring transducer enlarged to scale would lie wellover 500 kg, along with an installed length of more than 3000 mm and amaximum lateral expansion of more than 1000 mm. As a result, it can beunderstood that industrial grade, even series-manufacturable, measuringtransducers of conventional design and materials with nominal diametersof well over 300 mm will, both for reasons of technical feasibility anddue to economic considerations, not be available in the foreseeablefuture.

SUMMARY OF THE INVENTION

Based on the above recited state of the art, consequently, an object ofthe invention is to provide a measuring transducer suited for preciselymeasuring a viscosity or Reynolds number, also having a high accuracy ofmeasurement in the case of large mass flow rates of more as 1200 t/hand, associated therewith, large nominal diameters of over 100 mm, whileexhibiting a construction, which is as compact as possible.

For achieving the object, the invention resides in a measuring systemfor a medium flowing in a pipeline, for example, an aqueous liquid, aslurry, a paste or other flowing material. The measuring system, forinstance embodied as a compact measuring device and/or as a Coriolismass flow/viscosity measuring device, comprises a measuring transducerof vibration-type, through which the medium flows during operation, forproducing oscillation signals dependent on a viscosity and/or a Reynoldsnumber of the flowing medium, as well as a transmitter electronicselectrically coupled with the measuring transducer for driven themeasuring transducer and for evaluating the oscillation signalsdelivered by the measuring transducer. The measuring transducer includesan inlet-side, first flow divider with at least two flow openings spacedapart from one another, an outlet-side, second flow divider with atleast two flow openings spaced apart from one another, at least twostraight measuring tubes arranged parallel to one another for conveyingflowing medium and connected to the flow dividers, forming a tubearrangement with at least two flow paths connected for parallel flow.The measuring transducer also includes, as well, an electromechanicalexciter mechanism for exciting and maintaining mechanical oscillationsof the at least two measuring tubes, especially torsional oscillationsor torsional/bending oscillations, for example by means of a firstoscillation exciter acting on the at least two measuring tubes, and bymeans of a second oscillation exciter acting on the at least twomeasuring tubes. Of the at least two measuring tubes, a first measuringtube opens with an inlet-side, first measuring tube end into a firstflow opening of the first flow divider, and with an outlet-side, secondmeasuring tube end into a first flow opening of the second flow divider;and a second measuring tube, constructed equally to the first measuringtube in terms of shape, size, and material, opens with an inlet-side,first measuring tube end into a second flow opening of the first flowdivider, and with an outlet-side, second measuring tube end into asecond flow opening of the second flow divider. The transmitterelectronics feeds electrical excitation power into the exciter mechanismby means of a variable and/or, at least at times, periodic, firstelectrical driver signal supplied to the exciter mechanism, for example,with at least one signal frequency corresponding to an eigenfrequency ofa natural mode of oscillation of the tube arrangement, for instance,with a variable maximum voltage level and/or a variable maximumelectrical current level, while the exciter mechanism converts theelectrical excitation power, particularly dependent also on a voltagelevel and electrical current level of the first driver signal, at leastat times, at least partially, into torsional oscillations of the firstmeasuring tube and into torsional oscillations of the second measuringtube, which are opposite and equal (hereinafter opposite-equal) to thetorsional oscillations of the first measuring tube.

According to a first embodiment of the invention, it is additionallyprovided that the exciter mechanism converts the electrical excitationpower supplied by the transmitter electronics into torsionaloscillations of the first measuring tube, and into torsionaloscillations of the second measuring tube opposite-equal to thetorsional oscillations of the first measuring tube, in such a mannerthat a middle segment of the first measuring tube executes rotaryoscillations about an imaginary torsional oscillation axis perpendicularto a cross section of said tube segment, and a middle segment of thesecond measuring tube executes rotary oscillations about an imaginarytorsional oscillation axis perpendicular to a cross section of said tubesegment, and/or that the at least two measuring tubes executeopposite-equal torsional oscillations in a torsional oscillationfundamental mode having a single oscillatory antinode.

According to a second embodiment of the invention, it is additionallyprovided that the tube arrangement is embodied such that it has animaginary longitudinal section plane, in which extends a longitudinalaxis of the first measuring tube, which axis imaginarily connects thefirst and second ends of said first measuring tube, as well as alongitudinal axis of the second measuring tube, which axis imaginarilyconnects the first and second ends of said second measuring tube, andwhich axis extends parallel to the longitudinal axis of the firstmeasuring tube.

According to a third embodiment of the invention, it is additionallyprovided that the first measuring tube has a caliber which is equal to acaliber of the second measuring tube.

According to a fourth embodiment of the invention, it is additionallyprovided that the first oscillation exciter is so embodied and arrangedin the measuring transducer such that the line of action, with which theexciter forces produced by the first oscillation exciter are introducedinto the tube arrangement, has a perpendicular distance to the firstimaginary longitudinal section plane of the tube arrangement, which isgreater than a fourth of a caliber of the first measuring tube,especially greater than 35% of the caliber of the first measuring tube,and/or smaller than 200% of the caliber of the first measuring tube,especially smaller than 100% of the caliber of the first measuring tube.

According to a fifth embodiment of the invention, it is additionallyprovided that the exciter mechanism effects oscillations of themeasuring tubes, especially opposite-equal torsional oscillations of theat least two measuring tubes, or opposite-equal bending/torsionaloscillations of the at least two measuring tubes, by the feature that anexciter force acting on the first measuring tube, generated by means ofthe first oscillation exciter, acts opposite, especially opposite-equalto an exciter force acting on the second measuring tube, generatedsimultaneously by means of the first oscillation exciter.

According to a sixth embodiment of the invention, it is additionallyprovided that the exciter mechanism, for example, simultaneously to thetorsional oscillations, effects bending oscillations of the firstmeasuring tube about its longitudinal axis, and bending oscillations ofthe second measuring tube about its longitudinal axis opposite-equal tothe bending oscillations of the first measuring tube.

According to a seventh embodiment of the invention, it is additionallyprovided that the tube arrangement is embodied such that at least oneeigenfrequency of natural bending oscillations of the first measuringtube, especially in such a bending oscillation fundamental mode having asingle oscillatory antinode, equals an eigenfrequency of naturaltorsional oscillations of the first measuring tube, especially such in atorsional oscillation fundamental mode having a single oscillatoryantinode, and such that at least one eigenfrequency of natural bendingoscillations of the second measuring tube, especially such in a bendingoscillation fundamental mode having a single oscillatory antinode,equals an eigenfrequency of natural torsional oscillations of the secondmeasuring tube, especially such in a torsional oscillation fundamentalmode having a single oscillatory antinode.

According to an eighth embodiment of the invention, it is additionallyprovided that each of the at least two measuring tubes, excited by theexciter mechanism, executes opposite-equal bending oscillations,especially bending oscillations in a bending oscillation fundamentalmode having a single oscillatory antinode, coupled with, in each case,torsional oscillations of equal frequency, especially opposite-equaltorsional oscillations in a torsional oscillation fundamental modehaving a single oscillatory antinode.

According to a ninth embodiment of the invention, it is additionallyprovided that each of the at least two measuring tubes, excited by theexciter mechanism, executes opposite-equal bending oscillations with anoscillation frequency, which differs from an oscillation frequency ofthe opposite-equal torsional oscillations executed by the at least twomeasuring tubes, especially simultaneously to said bending oscillations,especially by more than 10% and/or by more than 50 Hz.

According to a tenth embodiment of the invention, it is additionallyprovided that the first driver signal has a plurality of signalcomponents with various signal frequencies, and wherein at least one ofthe signal components of the first driver signal, for example a dominantsignal component with respect to a signal power, has a signal frequencycorresponding to an eigenfrequency of a natural mode of oscillation ofthe tube arrangement, for example a natural torsional oscillation modeof the tube arrangement, in which mode the at least two measuring tubesexecute opposite-equal torsional oscillations.

According to an eleventh embodiment of the invention, it is additionallyprovided that, on the basis of an electrical excitation power,especially an electrical excitation power dependent on a voltage leveland an electrical current level of the first driver signal, converted inthe exciter mechanism, especially at least partially into torsionaloscillations of the at least two measuring tubes or at least partiallyin torsional/bending oscillations of the at least two measuring tubes,the transmitter electronics generates a measured value representing theviscosity of the flowing medium, and/or a measured value representingthe Reynolds number of the flowing medium.

According to a twelfth embodiment of the invention, it is additionallyprovided that, besides the first measuring tube and the second measuringtube, the measuring transducer has no additional measuring tube servingto convey flowing medium, and vibrating during operation.

According to a first further development of the invention, it isadditionally provided that the exciter mechanism has at least a firstoscillation exciter, for example an electrodynamic, first oscillationexciter, which, for example, acts differentially on the at least twomeasuring tubes, for converting electrical excitation power supplied tothe exciter mechanism into changing and/or periodic, mechanical exciterforces, for example forces having at least one signal frequencycorresponding to an eigenfrequency of a natural mode of oscillation ofthe tube arrangement, for effecting the torsional oscillations of thefirst measuring tube and the torsional oscillations of the secondmeasuring tube opposite-equal to the torsional oscillations of the firstmeasuring tube.

According to a first embodiment of the first further development of theinvention, it is additionally provided that the first oscillationexciter has a permanent magnet held on the first measuring tube, forexample, by means of a coupling element affixed to the first measuringtube and serving as a lever arm for effecting torsional moments that acton the first measuring tube, and a cylindrical coil permeated bymagnetic field of the permanent magnet, held on the second measuringtube, for instance, by means of a coupling element affixed to the secondmeasuring tube and serving as a lever arm for effecting torsionalmoments that act on the second measuring tube.

According to a second embodiment of the first further development of theinvention, it is additionally provided that the first driver signal issupplied to the first oscillation exciter, especially in such a mannerthat a first exciter current flows through its cylindrical coil, drivenby means of the variable first exciter voltage provided by the firstdriver signal.

According to a third embodiment of the first further development of theinvention, it is additionally provided that the first oscillationexciter converts an electrical excitation power converted therein, forinstance supplied by means of the first driver signal, into, for exampleperiodic, exciter forces serving to excite oscillations of the measuringtubes, for instance opposite-equal torsional oscillations of the atleast two measuring tubes, or opposite-equal bending/torsionaloscillations of the at least two measuring tubes. The exciter forces areintroduced in the tube arrangement along a line of action spaced fromand at least approximately parallel to an imaginary longitudinal sectionplane of the tube arrangement, for example, also a line of actionextending essentially transversely to the longitudinal axis of the firstmeasuring tube and to the longitudinal axis of the second measuringtube.

According to a second further development of the invention, it isadditionally provided that the transmitter electronics feeds electricalexcitation power into the exciter mechanism also by means of a variableand/or, at least at times, periodic, second electrical driver signalsupplied to the exciter mechanism, for example, a driver signal havingat least one signal frequency corresponding to an eigenfrequency of anatural mode of oscillation of the tube arrangement, and, for example, asecond driver signal equal to the first driver signal as regards atleast one signal frequency, and/or a second driver signal phase shiftedrelative to the first driver signal, for example, a second driver signalalso having a variable maximum voltage level and/or a variable maximumelectrical current level.

According to a first embodiment of the second further development of theinvention, it is additionally provided that the exciter mechanism alsoconverts electrical excitation power supplied by means of the seconddriver signal, especially electrical power dependent on a voltage leveland an electrical current level also of the second driver signal, atleast at times, into torsional oscillations of the first measuring tubeand to torsional oscillations of the second measuring tubeopposite-equal to the torsional oscillations of the first measuringtube, for example, in such a manner that a middle segment of the firstmeasuring tube executes rotary oscillations about an imaginary torsionaloscillation axis perpendicular to a cross section of said tube segment,and a middle segment of the second measuring tube executes rotaryoscillations about an imaginary torsional oscillation axis perpendicularto a cross section of said tube segment, and/or that the at least twomeasuring tubes execute opposite-equal torsional oscillations in atorsional oscillation fundamental mode having a single oscillatoryantinode.

According to a second embodiment of the second further development ofthe invention, it is additionally provided that the second driver signalhas a plurality of signal components with signal frequency varying fromone another, and that at least one of the signal components of thesecond driver signal, for example, a dominant signal component withrespect to a signal power, has a signal frequency corresponding to aneigenfrequency of a natural mode of oscillation of the tube arrangement,for example, a natural torsional oscillation mode of the tubearrangement, in which the at least two measuring tubes executeopposite-equal torsional oscillations.

According to a third embodiment of the second further development of theinvention, it is additionally provided that the second driver signal issupplied to an oscillation exciter of the exciter mechanism, forexample, in such a manner that a second exciter current passes through acylindrical coil of said oscillation exciter, driven by means of avariable second exciter voltage provided by the second driver signal.

According to a third further development of the invention, it isadditionally provided that the exciter mechanism further has a secondoscillation exciter, which is, for example, electrodynamic and/orequally constructed to the first oscillation exciter, and actsdifferentially on the at least two measuring tubes, for convertingelectrical excitation power supplied to the exciter mechanism intovariable and/or periodic, mechanical exciter forces, for example exciterforces having at least one signal frequency corresponding to aneigenfrequency of a natural mode of oscillation of the tube arrangement,effecting the torsional oscillations of the first measuring tube and thetorsional oscillations of the second measuring tube opposite-equal tothe torsional oscillations of the first measuring tube.

According to a first embodiment of the third further development of theinvention, it is additionally provided that the second oscillationexciter is formed from a permanent magnet held on the first measuringtube, for example by means of a coupling element affixed to the firstmeasuring tube and serving as a lever arm for effecting torsionalmoments which act on the first measuring tube, and from a cylindricalcoil permeated by the magnetic field of the permanent magnet, held onthe second measuring tube, for example, by means of a coupling elementaffixed to the second measuring tube, and serving as a lever arm foreffecting torsional moments which act on the second measuring tube.

According to a second embodiment of the third further development of theinvention, it is additionally provided that the second oscillationexciter is placed on a side of the first imaginary longitudinal sectionplane of the tube arrangement in the measuring transducer, which sidefaces away from the first oscillation exciter.

According to a third embodiment of the third further development of theinvention, it is additionally provided that the tube arrangement has animaginary cross sectional plane perpendicular to the imaginarylongitudinal section plane, in which cross sectional plane extend theline of action of the exciter forces produced by the first oscillationexciter, as well as the line of action of the exciter forces produced bythe second oscillation exciter.

According to a fourth embodiment of the third further development of theinvention, it is additionally provided that the exciter mechanismeffects oscillations of the measuring tubes, for example, opposite-equaltorsional oscillations of the at least two measuring tubes, oropposite-equal bending/torsional oscillations of the at least twomeasuring tubes, by the feature that an exciter force generated by meansof the second oscillation exciter, and acting on the first measuringtube, is directed oppositely, for example opposite-equal, to an exciterforce simultaneously generated by means of the second oscillationexciter, and acting on the second measuring tube.

According to a fifth embodiment of the third further development of theinvention, it is additionally provided that the exciter mechanismeffects opposite-equal torsional oscillations, for example,opposite-equal bending/torsional oscillations, of the at least twomeasuring tubes, by the features that the exciter force generated bymeans of the first oscillation exciter acting on the first measuringtube is directed oppositely to the exciter force generatedsimultaneously by means of the second oscillation exciter acting on thefirst measuring tube, and that the exciter force generated by means ofthe first oscillation exciter acting on the second measuring tube isdirected oppositely to the exciter force generated simultaneously bymeans of the second oscillation exciter acting on the second measuringtube. According to a sixth embodiment of the third further developmentof the invention, it is additionally provided that the secondoscillation exciter converts an electrical excitation power convertedtherein, supplied by means of a driver signal, into, for exampleperiodic, exciter forces serving to excite oscillations of the measuringtubes, for instance opposite-equal torsional oscillations of the atleast two measuring tubes, or opposite-equal bending/torsionaloscillations of the at least two measuring tubes. The exciter forces areintroduced in the tube arrangement along a line of action spaced fromand at least approximately parallel to an imaginary longitudinal sectionplane of the tube arrangement, for example also essentially parallel tothe line of action of exciter forces generated by means of the firstoscillation exciter, and/or extending essentially transversely to thelongitudinal axis of the first measuring tube and to the longitudinalaxis of the second measuring tube.

According to a fourth further development of the invention, themeasuring transducer further includes a sensor arrangement formed, forexample, by means of a first oscillation sensor and by means of anequally constructed second oscillation sensor, for, for example,differentially registering mechanical oscillations, for exampletorsional oscillations or torsion/bending oscillations, of the at leasttwo measuring tubes, and producing at least a first oscillation signalrepresenting mechanical oscillations, for example, torsionaloscillations or torsion/bending oscillations, of the at least twomeasuring tubes.

According to a first embodiment of the fourth further development of theinvention, it is provided that the first oscillatory signal delivered bythe sensor arrangement represents at least in part torsionaloscillations of the first measuring tube, for example, torsionaloscillations of the first measuring tube relative to opposite-equaltorsional oscillations of the second measuring tube.

According to a second embodiment of the fourth further development ofthe invention, it is provided that the transmitter electronics, by meansof the first oscillation signal, for example on the basis of a signalvoltage and/or a signal frequency of the first oscillation signal,generates the measured value representing the viscosity of the flowingmedium, and/or a measured value representing the Reynolds number of theflowing medium.

According to a third embodiment of the fourth further development of theinvention, the sensor arrangement includes at least a first oscillationsensor, which especially is electrodynamic and/or placed in themeasuring transducer on the inlet side, for, for example, differentiallyregistering, for example, inlet-side mechanical oscillations, especiallytorsional oscillations or torsion/bending oscillations of the at leasttwo measuring tubes, and for producing the first oscillation signal. Afurther development of this embodiment additionally provides that thefirst oscillation sensor has a permanent magnet held on the firstmeasuring tube, especially by means of a coupling element, and acylindrical coil permeated by the magnetic field of the permanentmagnet, held on the second measuring tube, for example by means of acoupling element, for producing an electrical voltage serving to formthe first oscillation signal of the sensor arrangement.

According to a fourth embodiment of the fourth further development ofthe invention, the sensor arrangement further includes two, for exampleelectrodynamic and/or equally constructed, oscillation sensors, and/or,in each case, oscillation sensors equally spaced from the firstoscillation exciter and/or placed in the measuring transducer ondifferent sides of the imaginary longitudinal section plane of the tubearrangement, and/or placed in the measuring transducer on the outletside, which sensors serve for registering, for example, differentiallyregistering, for example, outlet-side mechanical oscillations,especially torsional oscillations or torsion/bending oscillations of theat least two measuring tubes, and for the producing at least oneoscillation signal representing mechanical oscillations, especiallytorsional oscillations or torsion/bending oscillations, of the at leasttwo measuring tubes of the sensor arrangement. A further development ofthis embodiment additionally provides that each of the two oscillationsensors has a permanent magnet held on one of the measuring tubes, forexample, by means of a coupling element, and a cylindrical coilpermeated by the magnetic field of the permanent magnet, heldrespectively on the other measuring tube, for example, by means of acoupling element, for the producing an electrical voltage serving forforming an oscillation signal of the sensor arrangement.

According to a fifth embodiment of the fourth further development of theinvention, the sensor arrangement further includes four, for example,electrodynamic and/or equally constructed oscillation sensors, and/oroscillation sensors, in each case, equally spaced from the firstoscillation exciter, and/or placed in the measuring transducer ondifferent sides of the imaginary longitudinal section plane of the tubearrangement, which sensors serve for registering, for example, fordifferentially registering, mechanical oscillations, especiallytorsional oscillations or torsion/bending oscillations of the at leasttwo measuring tubes, and for the producing at least one oscillationsignal representing mechanical oscillations, especially torsionaloscillations or torsion/bending oscillations, of the at least twomeasuring tubes of the sensor arrangement. A further development of thisembodiment additionally provides that each of the four oscillationsensors has a permanent magnet held on one of the measuring tubes, forexample, by means of a coupling element, and a cylindrical coilpermeated by the magnetic field of the permanent magnet, heldrespectively on the other measuring tube, for example, by means of acoupling element, for the producing an electrical voltage serving forforming an oscillation signal of the sensor arrangement.

According to a fifth further development of the invention, the measuringtransducer includes further a first, for example plate shaped, couplingelement of first type affixed to the first measuring tube, for holdingcomponents of the first oscillation exciter, for example a cylindricalcoil or a permanent magnet, and for introducing an exciter forcegenerated by means of the first oscillation exciter into the firstmeasuring tube, and/or for transforming an exciter force generated bymeans of the first oscillation exciter into a torsional moment acting onthe first measuring tube, as well as a second coupling element of firsttype, for example a plate shaped, second coupling element of first typeand/or a second coupling element of first type equally constructed tothe first coupling element of first type, affixed to the secondmeasuring tube, for holding components of the first oscillation exciter,for example a cylindrical coil or a permanent magnet, and forintroducing an exciter force generated by means of the first oscillationexciter into the second measuring tube, and/or for transducing anexciter force generated by means of the first oscillation exciter into atorsional moment acting on the second measuring tube.

According to a sixth embodiment of the fifth further development of theinvention, it is provided that the oscillation exciter of the excitermechanism, in each case, is held on two coupling elements of first type,which lie oppositely to one another, especially in a manner such that aminimum distance between two coupling elements held on the sameoscillation exciter is more than twice as large as a tube outer diameterof the first measuring tube.

According to a seventh embodiment of the fifth further development ofthe invention, it is provided that a permanent magnet of the firstoscillation exciter is affixed to the first coupling element of firsttype, especially on a distal first end of the first coupling element offirst type removed from the first measuring tube, and a cylindrical coilof the first oscillation exciter is affixed to the second couplingelement of first type, for instance, on a distal first end of the secondcoupling element of first type removed from the second measuring tube,especially in such a manner that the first coupling element of firsttype acts as a lever arm, which converts an exciter force generated bythe first oscillation exciter at least partially into a torsional momenteffecting the torsional oscillations of the first measuring tube, andthat the second coupling element of first type acts as a lever arm,which converts an exciter force generated by the first oscillationexciter at least partially into a torsional moment effecting torsionaloscillations of the second measuring tube.

According to an eighth embodiment of the fifth further development ofthe invention, it is provided that the first and second couplingelements of first type are placed oppositely to one another in themeasuring transducer.

According to a ninth embodiment of the fifth further development of theinvention, it is provided that the first and second coupling elements offirst type are placed in the measuring transducer such that both acenter of mass of the first coupling element of first type as well as acenter of mass of the second coupling element of first type lie withinthe cross sectional plane, in which extend both the line of action ofthe exciter forces produced by the first oscillation exciter, as well asthe line of action of the exciter forces produced by the secondoscillation exciter. According to a tenth embodiment of the fifthfurther development of the invention, the measuring transducer furthercomprises

a third, for example plate shaped, coupling element of first typeaffixed to the first measuring tube, for holding components of the firstoscillation sensor, especially a cylindrical coil or a permanent magnet,and for transmitting to the oscillation sensor an oscillatory movementexecuted by the first measuring tube, and/or for converting a torsionaloscillation movement executed by the first measuring tube into atranslational movement dependent thereon;

a fourth coupling element of first type affixed to the second measuringtube, for example a plate shaped, fourth coupling element of first typeand/or a fourth coupling element of first type equally constructed tothe third coupling element of first type, for holding components of thefirst oscillation sensor, for example, a cylindrical coil or a permanentmagnet, and for transmitting to the oscillation sensor an oscillatorymovement executed by the second measuring tube, and/or for converting atorsional oscillation movement executed by the second measuring tubeinto a translational movement dependent thereon;

a fifth, for example plate shaped, coupling element of first type,affixed to the first measuring tube, for holding components of the firstoscillation sensor, for example, a cylindrical coil or a permanentmagnet, and for transmitting to the oscillation sensor an oscillatorymovement executed by the first measuring tube, and/or for converting atorsional oscillation movement executed by the first measuring tube intoa translational movement dependent thereon;

a sixth coupling element of first type affixed to the second measuringtube, for example a plate shaped, sixth coupling element of first typeand/or a sixth coupling element of first type equally constructed to thefifth coupling element of first type, for holding components of thesecond oscillation sensor, for example, a cylindrical coil or apermanent magnet, and for transmitting to the oscillation sensor anoscillatory movement executed by the second measuring tube, and/or forconverting a torsional oscillation movement executed by the secondmeasuring tube into a translational movement dependent thereon. Afurther development of this embodiment is additionally provides thateach of the, for example, equally constructed oscillation sensors of thesensor arrangement, in each case, is held on two coupling elements offirst type lying oppositely to one another, especially in such a manner,that a minimum distance between two oscillation sensors held on the samecoupling elements of first type is more than twice as large as a tubeouter diameter of the first measuring tube.

According to an eleventh embodiment of the fifth further development ofthe invention, the measuring transducer further comprises a first, forexample, plate shaped, coupling element of second type, which is affixedto the first measuring tube and to the second measuring tube andseparated on the inlet side from both the first flow divider as well asfrom the second flow divider for forming inlet-side oscillation nodes atleast for vibrations, for example, torsional oscillations or bendingoscillations or torsion/bending oscillations of the first measuring tubeand for vibrations of opposite phase thereto, for example, torsionaloscillations or bending oscillations or torsion/bending oscillations, ofthe second measuring tube, as well as a, for example, plate shaped,coupling element of second type, which is affixed to the first measuringtube and to the second measuring tube and separated on the outlet sidefrom both the first flow divider as well as from the second flow dividerfor forming outlet-side oscillation nodes at least for vibrations, forexample, torsional oscillations or bending oscillations ortorsion/bending oscillations of the first measuring tube and forvibrations of opposite phase thereto, for example, torsionaloscillations or bending oscillations or torsion/bending oscillations, ofthe second measuring tube.

According to a sixth further development of the invention, the measuringtransducer further includes a transducer housing, for example, anessentially tubular and/or outwardly circularly cylindrical transducerhousing, of which an inlet-side, first housing end is formed by means ofthe first flow divider, and an outlet-side, second housing end is formedby means of the second flow divider.

A basic idea of the invention is, instead of the conventional measuringsystems customarily used to the measure viscosity with a single straightmeasuring tube or two parallel bent measuring tubes through which themedium flows, to use two parallel straight measuring tubes through whichthe medium flows and which execute during operation at least partiallyopposite-equal torsional oscillations, and to enable such a high degreeof accuracy of measurement for viscosity, with, on the one hand, spacesaving construction of the measuring system as a whole, and also, on theother hand, acceptable pressure loss over a broad measuring range,especially also in the case of very high mass flow rates of well over1200 t/h.

An advantage of the measuring transducer of the invention isadditionally, among other things, that predominantly establishedstructural designs, as regards, for instance, the materials used, thejoining technology, the manufacturing steps, etc, can be applied or mustbe modified only slightly, whereby also the manufacturing costs, as awhole, are quite comparable to those of conventional measuringtransducers. In this respect, a further advantage of the invention canbe seen in the fact that thereby not only is an opportunity created tooffer comparatively compact measuring systems for viscosity also withlarge nominal diameters of over 100 mm, especially with a nominaldiameter of larger than 120 mm, with manageable geometric dimensions andempty masses, but in addition can be economically sensible to implement.Consequently, the measuring transducer of the invention is especiallysuitable for measuring flowing media, which are conveyed in a pipelinehaving a caliber of larger than 100 mm, especially of 150 mm or higher.In addition, the measuring transducer is also suitable for measuringmass flows, which, at least at times, are greater than 1200 t/h,especially at least, at times, more than 1400 t/h, such as can occure.g. in applications for measuring petroleum, natural gas or otherpetrochemical substances.

The invention as well as other advantageous embodiments thereof will nowbe explained in greater detail on the basis of examples of embodimentspresented in the figures of the drawing. Equal parts are provided in allfigures with equal reference characters; when required to avoidcluttering the drawing or when it otherwise appears sensible, alreadymentioned reference characters are omitted in subsequent figures. Otheradvantageous embodiments or further developments, particularly alsocombinations of firstly only individually explained aspects of theinvention, will become evident additionally from the figures of thedrawing.

BRIEF DESCRIPTION OF THE DRAWINGS

The figures of the drawing show as follows:

FIG. 1 a measuring system, for example, embodied as a Coriolis massflow/density/viscosity, measuring device in compact construction, inperspective, partially transparent, side view with a measuringtransducer of vibration-type and thereto connected transmitterelectronics;

FIG. 2 schematically in the manner of a block diagram, a transmitterelectronics, to which is connected a measuring transducer ofvibration-type for forming a measuring system according to FIG. 1;

FIG. 3 in, partially sectioned, or perspective, views, an example of anembodiment of a measuring transducer of vibration-type, especially onesuited for a measuring system according to FIG. 1, or 2;

FIGS. 4, 5, and 6 projections of a tube arrangement of the measuringtransducer according to FIG. 3 in different side views.

DETAILED DESCRIPTION IN CONJUNCTION WITH THE DRAWINGS

FIGS. 1, 2 show, schematically presented, a measuring system 1,especially one embodied as a Coriolis mass flow/viscosity, and/ordensity/viscosity, measuring device, serving to register a viscosity ηof a medium flowing in a pipeline (not shown) and to represent in theform of a measured value X_(η), or X_(RE) instantaneously representingsaid viscosity η—or also a therefrom derived, measured variable, suchas, for instance, a Reynolds number Re of the flow. The medium can bepractically any flowable material, for example, an aqueous or oil-likeliquid, a slurry, a paste or the like. Alternatively, or insupplementation, the inline measuring device 1 can, in given cases, alsobe used to measure a density rho and/or a mass flow m of the medium.Especially, the inline measuring device is provided, to measure media,such as e.g. petroleum or other petrochemical substances, which flow ina pipeline having a caliber of greater than 100 mm, especially a caliberof 150 mm or above. Especially, the inline measuring device isadditionally provided to measure flowing media of the aforementionedtype, which are caused to flow with a mass flow rate of greater than1200 t/h, especially greater than 1500 t/h. The measuring system, whichis here implemented, by way of example, by means of an inline measuringdevice in compact construction, comprises therefor: A measuringtransducer 11 of vibration-type connected via an inlet end as well as anoutlet end to the process line, through which measuring transducer flowsduring operation of the medium to be measured, such as, for instance, alow viscosity liquid and/or a high viscosity paste; as well as atransmitter electronics 12, which is electrically connected with themeasuring transducer 11, for instance, by means of a multi-veinedconnecting cable or corresponding single lines, and which, duringoperation, is supplied for example, from the exterior via connectingcable and/or by means of internal energy storer, with electrical energy,for driven the measuring transducer and for evaluating oscillatorysignals delivered by the measuring transducer.

The transmitter electronics 12 includes, as shown in FIG. 2schematically in the manner of a block diagram: A driver circuit Excserving for driven the measuring transducer; as well as a measuring, andevaluating, circuit μC processing primary signals of the measuringtransducer 11, for example, formed by means of a microcomputer and/orcommunicating during operation with the driver circuit Exc. Duringoperation, the measuring, and evaluating, circuit μC delivers measuredvalues representing the at least one measured variable, such as e.g. theviscosity and/or the Reynolds number, as well as, in given cases, othermeasured variables, such as the density and/or the instantaneous, or atotaled, mass flow of the flowing medium. The driver circuit Exc and theevaluating circuit μC, as well as other electronics components of thetransmitter electronics serving the operation of the measuring system,such as, for instance, internal energy supply circuits ESC for providinginternal supply voltages U_(N) and/or communication circuits COM servingfor connection to a superordinated measurement data processing systemand/or a fieldbus, are, in the here illustrated example of anembodiment, additionally accommodated in a—here single, especiallyimpact and/or also explosion resistantly and/or hermeticallysealed—electronics housing 7 ₂. For visualizing measuring systeminternally produced, measured values and/or, in given cases, measuringsystem internally generated, status reports, such as, for instance, anerror report or an alarm, onsite, the measuring system can, furthermore,have a display, and interactions, element HMI communicating, at least attimes, with the transmitter electronics, such as, for instance, a LCD-,OLED- or TFT-display placed in the electronics housing behind a windowcorrespondingly provided therein as well as a corresponding input keypadand/or a touch-screen. In advantageous manner, the, for example,(re-)programmable and/or remotely parameterable, transmitter electronics12 can additionally be so designed, that it can during operation of theinline measuring device exchange with a electronic data processingsystem superordinated thereto, for example, a programmable logiccontroller (PLC), a personal computer and/or a work station, via a datatransmission system, for example, a fieldbus system and/or wirelesslyper radio, measuring- and/or other operating data, such as, forinstance, current measured values or tuning- and/or diagnostic valuesserving the control of the inline measuring device. In such case, thetransmitter electronics 12 can have, for example, an internal energysupply circuit ESC, which is fed during operation via the aforementionedfieldbus system from an external energy supply provided in the dataprocessing system. In an embodiment of the invention, the transmitterelectronics is additionally so embodied, that it is connectableelectrically with the external electronic data processing system bymeans of a two-wire connection 2L configured, for example, as a 4-20mA-current loop, and can transmit thereby, measured values to the dataprocessing system, as well as being, in given cases, also supplied—atleast partially or exclusively—with electrical energy thereby. For thecase, in which the measuring system is to have the capability for acoupling to a fieldbus—or other communication system, the transmitterelectronics 12 can have a corresponding communication interface COM fordata communication according to one of the relevant industry standards.

In FIGS. 3, 4, 5, and 6, there is shown, supplementally to FIG. 1, or 2,in different representations, a measuring transducer 11 suited forreducing the measuring system of the invention to practice, in givencases, also applicable for mass flow- and/or density measuring. Thismeasuring transducer 11 is inserted during operation in the course of apipeline (not shown), through which medium to be measured flows. Themeasuring transducer 11 serves, as already mentioned, to produce in athrough flowing medium mechanical reaction forces, especially alsofrictional forces dependent on the viscosity of the medium, in givencases, also Coriolis forces dependent on the mass flow and/or inertialforces dependent on the density of the medium, which react measurably,especially registerably by sensor, on the measuring transducer, and toconvert such into primary signals—here embodied as oscillatorysignals—corresponding therewith. Based on these reaction forcesdescribing the flowing medium, or the therefrom derived, primary signalsof the measuring transducer, e.g. the viscosity η of the medium, themass flow, the density and/or therefrom derived measured variables, suchas, for instance, the Reynolds number Re can be measured by means ofevaluating methods correspondingly implemented in the transmitterelectronics.

The measuring transducer 11 includes—as directly evident from thecombined figures—a transducer housing 7 ₁—here essentially tubular, andoutwardly circularly cylindrical in form—serving, among other things,also as a support frame. In the housing, other components of themeasuring transducer 11 serving the registering of the at least onemeasured variable are accommodated protected against external,environmental influences. In the example of an embodiment shown here, atleast a middle segment of the transducer housing 7 ₁ is formed by meansof a straight, especially circularly cylindrical, tube, so that, for themanufacture of the transducer housing, for example, also cost effective,welded or cast, standard tubes, for example, of cast steel or forgedsteel, can be used. An inlet-side, first housing end of the transducerhousing 7 ₁ is formed by means of an inlet-side, first flow divider 20 ₁and an outlet-side, second housing end of the transducer housing 7 ₁ bymeans of an outlet-side, second flow divider 20 ₂. Each of the two flowdividers 20 ₁, 20 ₂, thus formed as integral components of the housing,includes in the here illustrated example of an embodiment exactly twoflow openings 20 _(1A), 20 _(1B), and 20 _(2A), 20 _(2B), respectively,in each case, spaced from one another, and embodied, for example,circularly cylindrically or conically, or, in each case, as inner cones.Moreover, each of the flow dividers 20 ₁, 20 ₂, manufactured, forexample, from steel, is provided with a flange 6 ₁, or 6 ₂, for example,of steel, for connecting the measuring transducer 11 to a tube segmentof the pipeline serving for supplying medium to the measuringtransducer, or to a tube segment of the mentioned pipeline serving forremoving medium from the measuring transducer. For leakage free,especially fluid tight, connecting of the measuring transducer with the,in each case, corresponding tube segment of the pipeline, each of theflanges includes additionally, a corresponding sealing surface 6 _(1A),or 6 _(2A), each of which is as planar as possible. A distance betweenthe two sealing surfaces 6 _(1A), 6 _(2A) of the two flanges defines,thus, for practical purposes, an installed length, L₁₁, of the measuringtransducer 11. The flanges are, especially as regards their innerdiameter, their respective sealing surfaces as well as the flange boresserving for accommodating corresponding connection bolts, dimensionedcorresponding to the nominal diameter D₁₁ provided for the measuringtransducer 11 as well as the, in given cases, relevant industrialstandards appropriate for a caliber of the pipeline, in whose course themeasuring transducer is to be used. As a result of the rather largenominal diameter of 100 mm or thereover ultimately desired for themeasuring transducer, its installed length L₁₁ amounts according to anembodiment of the invention to more than 800 mm. Additionally, it is,however, provided that the installed length of the measuring transducer11 is kept as small as possible, especially smaller than 3000 mm. Theflanges 6 ₁, 6 ₂ can, as well as also directly evident from FIG. 1 andas quite usual in the case of such measuring transducers, be arrangedtherefor as near as possible to the flow openings of the flow dividers20 ₁, 20 ₂, in order to so provide an as short as possible in-, oroutlet region in the flow dividers and, thus, as a whole, to provide anas short as possible installed length L₁₁ the measuring transducer,especially less than 3000 mm. For an as compact as possible measuringtransducer also combined with desired high mass flow rates of over 1200t/h, according to another embodiment of the invention, the installedlength and the nominal diameter of the measuring transducer are sodimensioned matched to one another, that a nominal diameter to installedlength ratio D₁₁/L₁₁ the measuring transducer, defined by a ratio of thenominal diameter D₁₁ the measuring transducer to the installed lengthL₁₁ the measuring transducer is smaller than 0.3, especially smallerthan 0.2 and/or greater than 0.1. In an additional embodiment of themeasuring transducer, the transducer housing has an essentially tubular,middle segment. Additionally, it is provided to so dimension thetransducer housing, that a housing inner diameter to nominal diameterratio of the measuring transducer defined by a ratio of the largesthousing inner diameter to the nominal diameter of the measuringtransducer is, indeed, greater than 0.9, however, smaller than 1.5, asmuch as possible, however, smaller than 1.2.

In the case of the here illustrated example of an embodiment, thereadjoin on the middle segment on the inlet side and on the outlet side,respectively, additionally likewise tubular end segments of thetransducer housing. For the case illustrated in the example of anembodiment, wherein the middle segment and the two end segments, as wellas also the respective flange-connected flow dividers in the inlet andoutlet regions, respectively, in each case, have the same innerdiameter, the transducer housing can in advantageous manner also beformed by means of a one piece, for example, cast or forged, tube, onwhose ends the flanges are formed or welded on, and wherein the flowdividers are formed by means of plates, especially plates somewhatspaced from the flanges, welded orbitally on the inner wall and/orwelded-on by means of laser, and having the flow openings. Especially,for the case, in which the mentioned housing inner diameter to nominaldiameter ratio of the measuring transducer is selected equal to one, formanufacture of the transducer housing, for example, a tube correspondingto the pipeline to be connected to as regards caliber, wall thicknessand material and, insofar, also correspondingly adapted as regards theallowed operating pressure, with length correspondingly matching theselected measuring tube length can be used. For simplifying thetransport of the measuring transducer, or the total therewith formed,inline measuring device, additionally, as, for example, also provided inthe initially mentioned U.S. Pat. No. 7,350,421, a transport eye can beprovided, affixed on the inlet side and on the outlet side on theexterior of the transducer housing.

For conveying the medium flowing, at least at times, through pipelineand measuring transducer, the measuring transducer of the inventioncomprises additionally at least—in the here illustrated example of anembodiment exactly—two (in the here illustrated example of anembodiment, exactly two), mutually parallel, straight, measuring tubes18 ₁, 18 ₂ held oscillatably in the transducer housing 10. Duringoperation, measuring tubes 18 ₁, 18 ₂, in each case, communicate withthe pipeline and are, at least at times, actively excited and caused tovibrate in at least one oscillatory mode suited for ascertaining thephysical, measured variable, the so-called driven, or also wanted, mode.Of the at least two—here essentially circularly cylindrical, and to oneanother as well as to the above mentioned middle tube segment of thetransducer housing parallel—measuring tubes, a first measuring tube 18 ₁opens with an inlet-side, first measuring tube end into a first flowopening 20 _(1A) of the first flow divider 20 ₁ and with an outlet-side,second measuring tube end into a first flow opening 20 _(2A) of thesecond flow divider 20 ₂ and a second measuring tube 18 ₂ opens with aninlet-side, first measuring tube end into a second flow opening 20 _(1B)of the first flow divider 20 ₁ and with an outlet-side, second measuringtube end into a second flow opening 20 _(2B) of the second flow divider20 ₂. The two measuring tubes 18 ₁, 18 ₂ are, thus, connected, in a tubearrangement having two flow paths providing parallel flow of medium, tothe flow dividers 20 ₁, 20 ₂, especially equally constructed flowdividers, and, indeed, in a manner enabling vibrations, especiallybending oscillations, of the measuring tubes relative to one another, aswell as also relative to the transducer housing, wherein said tubearrangement has an imaginary longitudinal section plane, in which extendboth a measuring tube, longitudinal axis of the first measuring tube,which imaginarily connects its first and second measuring tube ends, aswell as also a measuring tube, longitudinal axis of the second measuringtube, which imaginarily connects its first and second measuring tubeends and is parallel to the measuring tube, longitudinal axis of thefirst measuring tube. Especially, it is additionally provided, that themeasuring tubes 18 ₁, 18 ₂, as in the case of such measuring transducersquite usual, are held oscillatably in the transducer housing 7 ₁ only bymeans of said flow dividers 20 ₁, 20 ₂—thus, they have, apart from theelectrical connecting lines, otherwise no other mentionable mechanicalconnection to the transducer housing. Moreover, the first measuring tubehas, according to an additional embodiment of the invention, a caliber,which equals a caliber of the second measuring tube is.

The measuring tubes 18 ₁, 18 ₂, or the therewith formed, tubearrangement of the measuring transducer 11, are, as certainly alsodirectly evident from the combination of FIGS. 1, 3, 4 and 5, and asalso usual in the case of such measuring transducers, encased by thetransducer housing 7 ₁, in the illustrated instance, practicallycompletely encased. The transducer housing 7 ₁ serves, thus not only assupport frame or holder of the measuring tubes 18 ₁, 18 ₂ but, instead,moreover, also to protect these, as well as also other components placedwithin the transducer housing 7 ₁ of the measuring transducer, againstouter, environmental influences, such as e.g. dust or water spray.Moreover, the transducer housing 7 ₁ can additionally also be soexecuted and so dimensioned, that, it in the case of possible damage toone or more of the measuring tubes, e.g. through crack formation orbursting, outflowing medium can be completely retained up to a requiredmaximum positive pressure in the interior of the transducer housing 7 ₁for as long as possible, wherein such critical state can, as, forexample, mentioned also in the initially cited U.S. Pat. No. 7,392,709,be registered and signaled by means of corresponding pressure sensorsand/or on the basis of operating parameters internally produced by thementioned transmitter electronics during operation. Accordingly, used asmaterial for the transducer housing 7 ₁ can be, especially, steels, suchas, for instance, structural steel, or stainless steel, or also othersuitable high strength materials, or high strength materials usuallysuitable for this.

As material for the tube walls of the measuring tubes are, again,especially, titanium, zirconium or tantalum. Moreover, serving asmaterial for the measuring tubes 18 ₁, 18 ₂ can be, however, alsopractically any other, usually applied therefor or at least suitable,material, especially such having an as small as possible thermalexpansion coefficient and an as high as possible yield point. For mostapplications of industrial measurements technology, especially also inthe petrochemicals industry, consequently, also measuring tubes ofstainless steel, for example, also duplex steel or super duplex steel,would satisfy the requirements as regards mechanical strength, chemicalresistance as well as thermal requirements, so that, in numerous casesof application, the transducer housing 7 ₁, the flow dividers 20 ₁, 20₂, as well as also the tube walls of the measuring tubes 18 ₁, 18 ₂, ineach case, can be of steel of, in each case, sufficiently high quality,which can be of advantage, especially as regards material- andmanufacturing costs, as well as also the thermally related dilationbehavior of the measuring transducer 11 during operation. According toan embodiment, the measuring tubes 18 ₁, 18 ₂ of the invention are inadvantageous manner additionally so embodied and so installed in themeasuring transducer 11, that at least the minimum torsionaloscillation, resonance frequencies f_(t181), f_(t182) of the first andsecond measuring tubes 18 ₁, 18 ₂ are essentially equal to one another.Furthermore, it can be of advantage additionally to so construct and toso install the measuring tubes 18 ₁, 18 ₂ in the measuring transducer11, that at least also the minimum bending oscillation, resonancefrequencies f_(b181), f_(b182) of the first and second measuring tubes18 ₁, 18 ₂ are essentially equal to one another. Furthermore, the tubearrangement is additionally so embodied, that at least one eigen- orresonance frequency of natural bending oscillations of the firstmeasuring tube, for example, such in a bending oscillation, fundamentalmode having a single oscillatory antinode, equals an eigenfrequency ofnatural torsional oscillations of the first measuring tube, for example,such in a torsional oscillation, fundamental mode having a singleoscillatory antinode, and that at least one eigenfrequency of naturalbending oscillations of the second measuring tube, for instance, such ina bending oscillation, fundamental mode having a single oscillatoryantinode, equals an eigenfrequency of natural torsional oscillations ofthe second measuring tube, for instance, such in a torsionaloscillation, fundamental mode having a single oscillatory antinode.

As already mentioned, in the case of the measuring transducer 11, thereaction forces required for the measuring, especially the measuring ofviscosity and/or Reynolds number of the flowing medium, are effected inthe medium to be measured by causing the measuring tubes 18 ₁, 18 ₂ tooscillate in the so-called wanted, or driven, mode. In the case of themeasuring system of the invention, selected as wanted mode is anoscillatory mode wherein each of the measuring tubes executes, at leastpartially, torsional oscillations about an, in each case, associatedimaginary measuring tube longitudinal axis imaginarily connecting itsparticular measuring tube ends, for example, with a respective natural,torsional oscillation, resonance frequency intrinsic to the respectivemeasuring tube.

For exciting mechanical oscillations of the tube arrangement, thus, oftorsion- or torsion/bending oscillations of the measuring tubes, themeasuring transducer includes additionally an exciter mechanism 5 formedby means of at least a first, electromechanical, for example,electrodynamic, oscillation exciter acting—, for example,differentially—on the measuring tubes 18 ₁, 18 ₂, and serving to causeeach of the measuring tubes operationally, at least at times, to executesuitable mechanical oscillations in the wanted mode—namely, for example,torsional oscillations with a minimum torsional oscillation resonancefrequency, of the measuring tubes, and/or torsion/bending oscillations,about the particular imaginary measuring tube longitudinal axisimaginarily connecting the respective measuring tube ends—here, insofar,serving also as imaginary oscillation axis—with, in each case,sufficiently large oscillation amplitude for producing and registeringthe above named reaction forces in the medium, and, respectively, tomaintain said oscillations. The aforementioned torsion/bendingoscillations can, for example, be coupled oscillations, thusoscillations of equal frequency and standing in fixed phase relationshipto one another or, however, also simultaneously, or intermittently,executed torsion—and bending oscillations with different torsion—andbending oscillation frequencies. In accordance therewith, according toan additional embodiment of the invention, the exciter mechanism isdesigned also to effect, thus, actively to excite (in given cases, alsosimultaneously to the mentioned torsional oscillations of the twomeasuring tubes) bending oscillations of the first measuring tube aboutits measuring tube, longitudinal axis and bending oscillations of thesecond measuring tube about its measuring tube, longitudinal axisopposite-equal to the bending oscillations of the first measuring tube.

The at least one oscillation exciter of the exciter mechanism serves, insuch case, correspondingly to convert an electrical excitation powerP_(exc), fed into the exciter mechanism by the transmitter electronicsby means of a first electrical driver signal i_(exc1) supplied to theexciter mechanism, particularly also a power dependent on a voltagelevel and an electrical current level of the first driver signali_(exc1), namely into corresponding periodic, in given cases, alsoharmonic, exciter forces F_(exc1), which act as simultaneously anduniformly as possible, however, with opposite sense, on the measuringtubes 18 ₁, 18 ₂.

In the case of the measuring system of the invention, the excitermechanism formed by means of the at least one oscillation exciter—hereby means of two oscillation exciters placed, respectively, above andbelow the mentioned longitudinal section plane of the tube arrangement,for example, essentially equally constructed, oscillation exciters—is,especially, so embodied, that it converts the fed electrical excitationpower, as already indicated, at least at times, and/or at leastpartially, into torsional oscillations of the first measuring tube 18 ₁and thereto opposite-equal torsional oscillations of the secondmeasuring tube 18 ₂ (in the excited- or wanted mode). In an embodimentof the invention, it is, in such case, additionally provided, to convertelectrical excitation power fed from the transmitter electronics intothe exciter mechanism in such a manner into corresponding measuring tubeoscillations, that the at least two measuring tubes executeopposite-equal torsional oscillations in a torsional oscillation,fundamental mode having a single oscillatory antinode, at least,however, a middle tube segment of the first measuring tube executesrotary oscillations about an imaginary torsional oscillation axisperpendicular to a cross section of said tube segment and a middle tubesegment of the second measuring tube executes rotary oscillations aboutan imaginary torsional oscillation axis perpendicular to a cross sectionof said tube segment.

Additionally, it is provided, according to an embodiment of theinvention, that the at least one oscillation exciter is constructed asan oscillation exciter acting differentially on the two measuring tubes,namely that the exciter mechanism effects oscillations of the measuringtubes, thus, opposite-equal torsional oscillations of the at least twomeasuring tubes or opposite-equal bending/torsional oscillations of theat least two measuring tubes, by the feature that an exciter forcegenerated by means of the first oscillation exciter, acting on the firstmeasuring tube, is opposite, especially opposite-equal, to an exciterforce generated at the same time by means of the first oscillationexciter, acting on the second measuring tube. Additionally, the excitermechanism and the at least one driver signal i_(exc1) can, in such case,in advantageous manner, be embodied in such a manner and so matched toone another, that therewith the first measuring tube 18 ₁ and the secondmeasuring tube 18 ₂ are excited during operation, at least at times,—forexample, also simultaneously with the torsional oscillations—to oppositephase bending oscillations in a shared plane of oscillation—here, aplane of oscillation coplanar with the mentioned longitudinal sectionplane of the tube arrangement—, consequently essentially coplanarbending oscillations. Alternatively thereto or in supplementationthereof, the first oscillation exciter is additionally embodied as anoscillation exciter of electrodynamic type. In accordance therewith, theoscillation exciter includes, in the case of this embodiment, apermanent magnet held on the first measuring tube 18 ₁ and a cylindricalcoil held on the second measuring tube 18 ₂ and permeated by themagnetic field of the permanent magnet; especially, the oscillationexciter is embodied as a type of coil, plunger arrangement, in the caseof which the cylindrical coil is arranged coaxially to the permanentmagnet and the permanent magnet is embodied as a plunging armature movedwithin said cylindrical coil. Additionally, it is, in such case,provided, that the first driver signal i_(exc1) is fed to the firstoscillation exciter, or, in said oscillation exciter, electricalexcitation power correspondingly to be converted therein is fed in, inthat a first exciter current flows through the cylindrical coil of theoscillation exciter driven by a variable first exciter voltage providedby means of the driver signal.

In an additional embodiment of the invention, the at least oneoscillation exciter is so embodied and placed on the tube arrangement,that the therewith produced—here essentially translational—exciterforces F_(exc1) are introduced along an imaginary line of action intothe tube arrangement spaced from the mentioned imaginary longitudinalsection plane and, apart from a principle of action related slightcurvature and a component tolerance related, slight offset, extending atleast approximately parallel thereto, for example, also essentiallytransversely to the measuring tube, longitudinal axis of the firstmeasuring tube and to the measuring tube, longitudinal axis of thesecond measuring tube, and, as a result, there can be produced in eachof the measuring tubes corresponding torsional moments M₁₈₁, M₁₈₂ aboutthe associated measuring tube, longitudinal axes. Especially, the firstoscillation exciter 5 ₁ is, in such case, so embodied and arranged inthe measuring transducer, that the line of action, with which theexciter forces produced by the first oscillation exciter are introducedinto the tube arrangement, has a perpendicular distance to the imaginarylongitudinal section plane of the tube arrangement, which is greaterthan a fourth of the caliber of the first measuring tube, especiallygreater than 35% of the caliber of the first measuring tube, and/orsmaller than 200% of the caliber of the first measuring tube, especiallysmaller than 100% of the caliber of the first measuring tube.

Particularly also for the purpose of implementing the aforementionedspacing of the at least one oscillation exciter from, in each case, thefirst and second measuring tubes, especially also a spacing serving forthe conversion of essentially translational exciter forces produced onthe part of the at least one oscillation exciter into torsional moments,the measuring transducer, according to an additional embodiment of theinvention, comprises additionally a first coupling element 25 ₁ of firsttype affixed only to the first measuring tube, for example, anessentially plate shaped, first coupling element 25 ₁ of first type, forholding components of the first oscillation exciter, for example, acylindrical coil or a permanent magnet, and for introducing an exciterforce generated by means of the first oscillation exciter into the firstmeasuring tube and/or for converting an exciter force generated by meansof the first oscillation exciter into a torsional moment acting on thefirst measuring tube, as well as a second coupling element 25 ₁ of firsttype affixed only to the second measuring tube, for example, anessentially plate shaped, second coupling element 25 ₁ of first typeand/or a second coupling element 25 ₁ of first type constructed equallyto the first coupling element 25 ₁ of first type, for holding componentsof the first oscillation exciter, for example, thus a cylindrical coil,or a permanent magnet, and for introducing an exciter force generated bymeans of the first oscillation exciter into the second measuring tubeand/or for converting an exciter force generated by means of the firstoscillation exciter into a torsional moment acting on the secondmeasuring tube. As directly evident from the combination of FIGS. 1, 3and 4, the first and second coupling elements 25 ₁, 25 ₂ of first typeare as much as possible oppositely lying to one another, however, placedspaced from one another in the measuring transducer 11 in a mannerenabling relative oscillatory movements of the measuring tubes.Furthermore, in the here illustrated example of an embodiment, the firstand second coupling elements of first type are, in eachcase,—consequently also the oscillation exciter held thereby—arranged inthe region of, for instance, half the free oscillatory length of therespective measuring tubes. By means of the two coupling elements 25 ₁,25 ₂ of first type holding the at least one oscillation exciter, it canbe assured in very effective, equally as well very simple, manner, thatthe exciter force generated by means of the oscillation exciter 5 ₁ caneffect equal frequency torsion—and bending oscillations of the measuringtubes, with the oscillations having a fixed phase relationship relativeto one another.

Additionally, in an additional embodiment of the invention, particularlyalso for the mentioned case, in which the oscillation exciter is ofelectrodynamic type, a permanent magnet serving as a component of theoscillation exciter is held to the first measuring tube by means of thecoupling element of first type—here also serving as a lever armeffecting torsional moments acting on the first measuring tube—affixedto the first measuring tube, for instance, at a, distal first end of thefirst coupling element 25 ₁ of first type removed from the firstmeasuring tube. Furthermore, also a cylindrical coil permeated by themagnetic field of said permanent magnet and serving as another componentof the oscillation exciter is held to the second measuring tube by meansof the coupling element of first type—here also serving as a lever armeffecting torsional moments acting on the second measuring tube—affixedto the second measuring tube, for instance, at a, distal first end ofthe second coupling element 25 ₂ of first type removed from the secondmeasuring tube.

According to an additional embodiment of the invention, the at least onedriver signal i_(exc1) is additionally so embodied, that it, at least attimes, thus at least over a period of time sufficient for ascertainingat least one viscosity, measured value, is periodically variable and/orvariable with at least one signal frequency corresponding to aneigenfrequency of a natural mode of oscillation of the tube arrangement,consequently the torsional oscillation, resonance frequency of thewanted mode selected for the measuring. The at least one driver signaland, insofar, the therewith produced, exciter forces F_(exc1) can, insuch case, in manner known, per se, to those skilled in the art, e.g. bymeans of an electrical current—and/or voltage control circuit providedin the already mentioned measuring—and operating electronics, be tunedas regards their amplitude and, e.g. by means of a phase control loop(PLL) likewise provided in the transmitter electronics, as regards theirfrequency (compare, for this, for example, also U.S. Pat. No. 4,801,897or U.S. Pat. No. 6,311,136), so that thus the driver signal has avariable maximum voltage level and/or a variable maximum electricalcurrent level, particularly such also correspondingly matched to theactually required excitation power. In such case, the first driversignal i_(exc1) can also be so embodied, that it has a plurality ofsignal components of mutually differing signal frequencies, and that atleast one of the signal components, for instance, a signal componentdominating as regards signal power. The first driver signal i_(exc1) hasa signal frequency corresponding to an eigenfrequency of a natural modeof oscillation of the tube arrangement, for example, thus thateigenfrequency of the selected wanted mode, consequently that of thenatural torsional oscillation mode of the tube arrangement, in which theat least two measuring tubes execute opposite-equal torsionaloscillations.

According to a further development of the invention, the transmitterelectronics is additionally designed to supply the exciter mechanismelectrical excitation power also by means of a variable and/or, at leastat times, periodic, second electrical driver signal i_(exc2), forexample, having at least one signal frequency corresponding to aneigenfrequency of a natural mode of oscillation of the tube arrangement,so that the exciter mechanism, as a result of this, also convertselectrical excitation power, then also dependent on a voltage level andan electrical current level also of the second driver signal, as fed bymeans of the second driver signal, at least at times, into the mentionedtorsional oscillations of the first measuring tube and the theretoopposite-equal torsional oscillations of the second measuring tube. Thesecond driver signal can, in such case, likewise have a plurality ofsignal components of mutually differing signal frequencies, of which atleast one signal component—, for instance, a signal component dominatingas regards signal power—has a signal frequency corresponding to aneigenfrequency of a natural mode of oscillation of the tube arrangement,especially an eigenfrequency of a natural torsional oscillation mode ofthe tube arrangement, in which the at least two measuring tubes executeopposite-equal torsional oscillations. According to an additionalembodiment of the invention, the second electrical driver signali_(exc2) (especially one produced simultaneously to the first driversignal) is, as regards at least one signal frequency, equal to the firstdriver signal, especially in such a manner, that a signal component ofthe first driver signal dominating as regards electrical current levelhas the same frequency as a signal component of the second driver signaldominating as regards electrical current level. In supplementationthereto, it is additionally provided, that the second electrical driversignal is fed into the exciter mechanism, at least at times,phase-shifted relative to the first driver signal, for example, by aphase angle lying in the range of 90° to 180° or by a phase angle ofexactly 180 deg, or at least the two driver signals are so arranged, atleast at times, as regards their phase relationship relative to oneanother, that the electrical current level dominating signal componentof the first driver signal has, for example, a phase angle lying in arange of 90° to 180° lies or exactly 180° relative to the maximumelectrical current level dominating signal component of the seconddriver signal, or, that is to say, phase-shifted as regards the signalpower dominating signal components. Moreover, it can be quiteadvantageous to make the second electrical driver signal variable, ingiven cases, also adjustable during operation, as regards its maximumvoltage level and/or its maximum electrical current level.Alternatively, or in supplementation, to the application of driversignals phase shifted relative to one another, according to anadditional embodiment of the invention, particularly also for thepurpose of an exciting of coupled torsion/bending oscillations of themeasuring tubes, it is provided that the second electrical driver signalis supplied into the exciter mechanism, at least at times, with asmaller maximum electrical current level in comparison to the firstdriver signal, at least, however, the two driver signals are so matchedrelative to one another, that the signal component of the first driversignal dominating as regards the electrical current level has, at leastat times, a signal power, which is, for example, larger by more than30%, than the signal power of the signal component of the second driversignal dominating as regards the electrical current level, so that, as aresult, the exciter force F_(exc1) produced by means of the firstoscillation exciter, at least at times, has a size, which is differentfrom a size of the exciter force F_(exc2) produced by means of thesecond oscillation exciter, and/or that the torsional moment produced bymeans of the first oscillation exciter lastly likewise in the first andsecond measuring tubes, in each case, has, in each case, at least attimes, a magnitude, which is different from a magnitude of a torsionalmoment produced by means of the second oscillation excitersimultaneously in the first, or second measuring tube.

According to an additional embodiment of the invention, tube and thethereon acting exciter mechanism are so embodied and the at least onefed driver signal i_(exc1), at least at times, so matched to tube andexciter mechanism, that each of the at least two measuring tubes,excited by the exciter mechanism, during operation, at least at times,executes opposite-equal bending oscillations, for example, bendingoscillations in a bending oscillation, fundamental mode having a singleoscillatory antinode, in given cases, also simultaneously with theactively excited torsional oscillations. The bending oscillations can,in such case, be coupled, for example, in each case, with torsionaloscillations of equal frequency thereto, for instance, opposite-equaltorsional oscillations in a torsional oscillation, fundamental modehaving a single oscillatory antinode. Alternatively thereto, tube andexciter mechanism as well as the at least one driver signal can beembodied so matched to one another, that each of the at least twomeasuring tubes, excited by the exciter mechanism, executesopposite-equal bending oscillations with an oscillation frequency, whichdiffers from an oscillation frequency of the of the at least twomeasuring tubes, especially opposite-equal torsional oscillationsexecuted simultaneously to said bending oscillations, for instance, bymore than 10% and/or by more than 50 Hz. In an additional embodiment ofthe invention, the measuring tubes 18 ₁, 18 ₂ are excited by means ofthe exciter mechanism 5 during operation at least partially to bendingoscillations, which have a bending oscillation frequency, which isapproximately equal to an instantaneous mechanical resonance frequencyof the measuring tubes 18 ₁, 18 ₂, or the therewith formed, tubearrangement, or which lies at least in the vicinity of such an eigen- orresonance frequency. The instantaneous, mechanical bending oscillation,resonance frequencies are, as is known, in special measure, dependent onsize, shape and material of the measuring tubes 18 ₁, 18 ₂,particularly, however, also on an instantaneous density of the mediumflowing through the measuring tubes and can, insofar, be variable duringoperation of the measuring transducer within a wanted-frequency band ofquite a few hertz. In the case of exciting the measuring tubes tobending oscillation resonance frequency, on the one hand, on the basisof the instantaneously excited oscillation frequency, supplementallyalso an average density of the medium flowing instantaneously throughthe measuring tubes can be easily ascertained. On the other hand, inthis way, also the electrical power instantaneously required formaintaining the excited oscillations can be minimized.

Especially, the measuring tubes 18 ₁, 18 ₂, driven by the excitermechanism 5, additionally, are caused to oscillate, at least at times,with essentially equal oscillation frequency, especially at a sharednatural mechanical eigenfrequency of the tube arrangement. Especiallysuited here is a bending oscillation, fundamental mode naturallyinherent to each of the measuring tubes 18 ₁, or 18 ₂, and having atminimum bending oscillation, resonance frequency, f18 ₁, or f18 ₂,exactly one bending-oscillation antinode. For example, the measuringtubes 18 ₁, 18 ₂, can be excited during operation by the thereto held,electromechanical exciter mechanism to bending oscillations, especiallyat an instantaneous mechanical eigenfrequency of the tube arrangementformed by means of the measuring tubes 18 ₁, 18 ₂, in the case of whichthey—at least predominantly—are caused to oscillate laterally deflectedin a respective plane of oscillation and, as directly evident from thecombination of FIGS. 1, 3, 4 and 5, in a shared plane of oscillation XZ1with essentially opposite phase to one another. This especially in sucha manner, that each of the measuring tubes 18 ₁, 18 ₂, executes duringoperation, at the same time, vibrations embodied, at least at times,and/or at least partially, in each case, as bending oscillations about ameasuring tube, longitudinal axis imaginarily connecting the first andthe, in each case, associated second measuring tube end of therespective measuring tube, wherein the measuring tube, longitudinal axesin the here illustrated example of an embodiment with mutually parallelmeasuring tubes 18 ₁, 18 ₂, extend equally parallel to one another, asthe measuring tubes 18 ₁, 18 ₂, and, moreover, also essentially parallelto an imaginary longitudinal axis of the total measuring transducerimaginarily connecting the two flow dividers and extending through acenter of mass of the tube arrangement. In other words, the measuringtubes can, as quite usual in the case of measuring transducers ofvibration-type, be caused to oscillate, in each case, at leastsectionally in a bending oscillation mode in the manner of a stringclamped at both sides. Accordingly, are according to an additionalembodiment, the first and second measuring tubes 18 ₁, 18 ₂, are caused,in each case, to execute bending oscillations, which lie in a sharedplane of oscillation XZ1 and, insofar, are embodied essentiallycoplanarly. As a result of medium flowing through the measuring tubesexcited to bending oscillations, there are induced therein additionallyalso Coriolis forces dependent on the mass flow, which effect, in turn,additional deformations of the measuring tubes, which correspond tohigher oscillation modes of the measuring tubes—the so-called Coriolismode—, and which are registerable by sensor. In advantageous manner, theoscillatory behavior of the tube arrangement formed by means of themeasuring tubes 18 ₁, 18 ₂, —together with the exciter mechanism and thesensor arrangement—, as well as also the driver signals controlling theexciter mechanism can, in such case, additionally be so matched to oneanother, that, as already indicated, at least the actively excitedoscillations of the measuring tubes 18 ₁, 18 ₂, are so embodied, thatthe first and the second measuring tubes 18 ₁, 18 ₂ execute bothtorsional oscillations of essentially opposite phase to one another,thus opposite-equal torsional oscillations with an opposing phase shiftof, for instance, 180 deg, as well as also bending oscillations ofessentially opposite phase to one another.

According to another further development of the invention,—as alreadyindicated—the exciter mechanism includes, particularly also for thepurpose of increasing the robustness, or stability, with which theoscillations in the wanted mode actually are excited and/or for thepurpose of the—simultaneous or alternative—exciting of torsion—andbending oscillations, further a second oscillation exciter acting on theat least two measuring tubes—here likewise differentially—, for example,an electrodynamic, second oscillation exciter or one constructed equallyto the first oscillation exciter, for converting electrical excitationpower fed into the exciter mechanism into mechanical exciter forcesF_(exc2) effecting the torsional oscillations of the first measuringtube 18 ₁ and the torsional oscillations of the second measuring tube 18₂ opposite-equal to the torsional oscillations of the first measuringtube 18 ₁. The exciter forces produced by means of the secondoscillation exciter—here periodically at least over a sufficiently longperiod of time for ascertaining a viscosity, measured value—are,according to an additional embodiment of the invention, variable with atleast one signal frequency corresponding to an eigenfrequency of anatural mode of oscillation of the tube arrangement. Furthermore, alsothe second oscillation exciter can in advantageous manner be so embodiedand placed on the tube arrangement, that the therewith produced exciterforces F_(exc2) are introduced into the tube arrangement along animaginary line of action spaced from the mentioned imaginarylongitudinal section plane and extending at least approximately parallelthereto, for example, also essentially transversely to the measuringtube, longitudinal axis of the first measuring tube and to the measuringtube, longitudinal axis of the second measuring tube, and, as a resultof this, in each of the measuring tubes, corresponding torsional momentsare produced about the particular measuring tube, longitudinal axes. Asdirectly evident from the combination of FIGS. 1, 3 and 4, the secondoscillation exciter 5 ₂ is placed in the measuring transducer for thison a side of the imaginary longitudinal section plane of the tubearrangement facing away from the first oscillation exciter 5 ₁.

Especially, according to an additional embodiment, at least the firstoscillation exciter 5 ₁ is additionally so embodied and arranged in themeasuring transducer, that the line of action, with which the producedexciter forces by said oscillation exciter 5 ₁ are introduced into thetube arrangement, has a perpendicular distance to the imaginarylongitudinal section plane of the tube arrangement, which is greaterthan a fourth of the caliber of the first measuring tube, especiallygreater than 35% of the caliber of the first measuring tube, and/orsmaller than 200% of the caliber of the first measuring tube, especiallysmaller than 100% of the caliber of the first measuring tube. In theexample of an embodiment shown here, the two oscillation exciters areadditionally so placed in the measuring transducer, that the firstoscillation exciter is arranged above the longitudinal section plane ofthe tube arrangement, insofar, also spaced from a center of mass of thetube arrangement, and the second oscillation exciter is arranged belowsaid longitudinal section plane, insofar, equally spaced from saidcenter of mass of the tube arrangement, —here in, in each case, equaldistanced from the longitudinal section plane. For producing differentlylarge torsional moments—, for example, also for the purpose of excitingcoupled torsion/bending oscillations—the two oscillation exciters can,however, also be placed with different distances to longitudinal sectionplane, or center of mass, of the tube arrangement.

For the mentioned case, in which the measuring transducer has couplingelements 25 ₁, 25 ₂ of first type, besides the first oscillation exciter5 ₁ also the second oscillation exciter 5 ₂ can be correspondingly heldthereto, for example, also in such a manner, that, as directly evidentfrom FIG. 1, or 4, a minimum distance between the first and secondoscillation exciters 5 ₁, 5 ₂, in total, more than 1.5-times as large asa pipe outer diameter of the measuring tubes 18 ₁, 18 ₂, at least,however, of the first measuring tube 18 ₁. In this way, as a whole, anoptimal exploitation of the space available in the interior of thetransducer housing 7 ₁, as well as also a high effectiveness of theoscillation exciter 5 ₁, 5 ₂, are attainable. Particularly also for thementioned case, in which the second oscillation exciter, or each of thetwo oscillation exciter 5 ₁, 5 ₂, is of electrodynamic type, in anadditional embodiment of the invention, a permanent magnet serving as acomponent of the second oscillation exciter is held affixed to the firstmeasuring tube by means of the first coupling element of firsttype—here, again, serving as a lever arm effecting torsional momentsacting on the first measuring tube—, and a cylindrical coil serving asanother component of the second oscillation exciter and permeated by themagnetic field of said permanent magnet is held affixed to the secondmeasuring tube by means of the second coupling element of firsttype—here, again, serving as lever arm effecting torsional momentsacting on the second measuring tube—. In advantageous manner, the firstand second coupling elements 25 ₁, 25 ₂ of first type, in such case, areadditionally so placed in the measuring transducer, that both a centerof mass of the first coupling element 25 ₁ of first type as well as alsoa center of mass of the second coupling element 25 ₂ of first type liewithin an imaginary cross sectional plane of the tube arrangement, inwhich extend both the line of action of the exciter forces produced bythe first oscillation exciter, as well as also the line of action of theexciter forces produced by the second oscillation exciter. As a result,thus, in such case, each of the, especially equally constructed,oscillation exciters 5 ₁; 5 ₂, is, in each case, equally held on the twocoupling elements 25 ₁, 25 ₂ of first type lying opposite one another,so that thus the measuring transducer quite resembles that illustratedin the initially mentioned WO-A 2009/120223 or US-A 2007/0151368,however, among other things, with the major difference, that, in thecase of the measuring transducer of the measuring system of theinvention, among other things, the exciter forces F_(exc1) produced bymeans of the first oscillation exciter act relative to the exciterforces F_(exc2) produced by means of the second oscillation exciter atleast partially and/or, at least at times, oppositely and/or withdifferent intensity on the tube arrangement and, as a result of this,torsional oscillations of the measuring tubes are actively excited.Additionally, in the case of application of the second oscillationexciter according to an additional embodiment of the invention, it isprovided that the second driver signal i_(exc2) is fed to the secondoscillation exciter, or electrical excitation power correspondingly tobe converted therein is fed in, by the fact that a second excitercurrent flows through the cylindrical coil of the second oscillationexciter driven by a variable second exciter voltage provided by means ofthe second driver signal.

As evident from FIGS. 1, 2, 3 and 5 and usual in the case of measuringtransducers of the type being discussed, there is provided in themeasuring transducer 11 additionally a sensor arrangement 19 formed bymeans of at least a first oscillation sensor, for example, anelectrodynamic, first oscillation sensor, reacting to, for example,inlet- or outlet-side, vibrations, particularly also to theopposite-equal torsion oscillations or torsion/bending oscillations, ofthe measuring tubes 18 ₁, 18 ₂ excited by means of the exciter mechanism5. The sensor arrangement 19 registers, for example, differentially,mechanical oscillations, particularly also torsional oscillations ortorsion/bending oscillations, of the at least two measuring tubes 18 ₁,18 ₂, and produces, for representing mechanical oscillations,particularly torsional oscillations, in given cases, also bendingoscillations, of the measuring tubes, at least one oscillationmeasurement signal u_(sens1), which represents at least partiallytorsional oscillations of the first measuring tube 18 ₁, particularlyalso the excited torsional oscillations of the same relative toopposite-equal torsional oscillations of the second measuring tube 18 ₂,and which as regards at least one signal parameter, for example, afrequency, a signal amplitude, consequently a signal voltage, and/or aphase relationship relative to the at least one driver signal i_(exc1),is influenced by the measured variable to be registered, such as, forinstance, the viscosity of the medium, the density and the mass flowrate.

In an additional embodiment of the invention, the sensor arrangement isformed by means of a first oscillation sensor 19 ₁, for example, anelectrodynamic, first oscillation sensor, differentially registeringtorsional oscillations or torsion/bending oscillations of the firstmeasuring tube 18 ₁ relative to the second measuring tube 18 ₂ as wellas by a second oscillation sensor 19 ₂, for example, an electrodynamic,second oscillation sensor, differentially registering torsionaloscillations or torsion/bending oscillations of the first measuring tube18 ₁ relative to the second measuring tube 18 ₂, which two oscillationsensors, reacting, in each case, to movements of the measuring tubes 18₁, 18 ₂, especially their torsional oscillation related twisting, ordeformations, in given cases, however, also to lateral deflections ofthe measuring tubes, deliver the first oscillation measurement signalU_(sens1), or a second oscillation measurement signal U_(sens2). This,for example, also in such a manner, that the at least two oscillationmeasurement signals U_(sens1), U_(sens2) delivered by the sensorarrangement 19 have a phase shift relative to one another, whichcorresponds to, or is dependent thereon, the instantaneous mass flowrate of the medium flowing through the measuring tubes, as well as, ineach case, have a signal frequency, which depends on an instantaneousdensity of the medium flowing in the measuring tubes. The firstoscillation sensor 19 ₁ can, in such case, be placed, for example, onthe inlet side of the measuring tubes. Equally, also the secondoscillation sensor 19 ₂ can be arranged on the inlet side of themeasuring tubes, for instance, in such a manner, that the firstoscillation sensor is placed above the imaginary longitudinal sectionplane of the tube arrangement and the second oscillation sensor oppositethe first oscillation sensor below said longitudinal section plane.Alternatively thereto, the second oscillation sensor 19 ₂ can, however,also be arranged on the outlet side of the at least two measuring tubes,for instance, in such a manner, that the two, for example, one anotherequally constructed, oscillation sensors 19 ₁, 19 ₂—as in the case ofmeasuring transducers of the type being discussed quite usual—are placedessentially equidistant in the measuring transducer 11 from the at leastone oscillation exciter 5 ₁, thus, in each case, equally as far removedfrom said oscillation exciter 5 ₁. For assuring an as high as possiblesensitivity of the measuring transducer, particularly also to the massflow registered, in given cases, by means of bending oscillations of themeasuring tubes, according to an additional embodiment of the invention,the measuring tubes the oscillation sensors are, in such case, soarranged in the measuring transducer, that a measuring length, L₁₉, ofthe measuring transducer corresponding to a minimum distance between thefirst oscillation sensor 19 ₁ and the second oscillation sensor 19 ₂amounts to more than 500 mm, especially more than 600 mm.

Moreover, the oscillation sensors of the sensor arrangement 19 can be ofequal construction to the at least one oscillation exciter of theexciter mechanism 5, at least to the extent that they work analogouslyto its principle of action, for example, thus likewise are ofelectrodynamic type and/or are held on the measuring tubes, removed fromthe longitudinal section plane of the tube arrangement, by means ofcoupling elements of first type serving as lever arms. Accordingly, themeasuring transducer, especially for the mentioned case, in which the atleast one oscillation exciter is held by means of two coupling elements25 ₁, 25 ₂ of first type on the at least two measuring tubes,additionally includes a third coupling element 25 ₃ of first type, forexample, a plate shaped, third coupling element, affixed to the firstmeasuring tube for holding components of the first oscillation sensor,for instance, a cylindrical coil for producing an electrical voltageserving for forming the first oscillation signal, or a permanent magnet,and for transmitting to the oscillation sensor an oscillatory movementexecuted by the first measuring tube, particularly also for converting atorsional oscillation movement executed by the first measuring tube intoa translational movement dependent thereon, a fourth coupling element 25₄ of first type, for example, a plate shaped, fourth coupling element ora fourth coupling element of equal construction to the third couplingelement 25 ₃ of first type, affixed to the second measuring tube forholding components of the first oscillation sensor, for instance, acylindrical coil or a permanent magnet, and for transmitting to theoscillation sensor an oscillatory movement executed by the secondmeasuring tube, or for converting a torsional oscillation movementexecuted by the first measuring tube into a translational movementdependent thereon, a fifth coupling element 25 ₅ of first type, forexample, a plate shaped, fifth coupling element, affixed to the firstmeasuring tube for holding components of the second oscillation sensor,for instance, a cylindrical coil for producing an electrical voltageserving for forming the second oscillation signal, or a permanentmagnet, and for transmitting to the oscillation sensor an oscillatorymovement executed by the first measuring tube, or for converting atorsional oscillation movement executed by the first measuring tube intoa translational movement dependent thereon, as well as a sixth couplingelement 25 ₆ of first type, for example, a plate shaped, sixth couplingelement or a sixth coupling element of equal construction to the fifthcoupling element 25 ₅ of first type, affixed to the second measuringtube for holding components of the second oscillation sensor, forinstance, a cylindrical coil or a permanent magnet, and for transmittingto the oscillation sensor an oscillatory movement executed by the secondmeasuring tube, or for converting a torsional oscillation movementexecuted by the first measuring tube into a translational movementdependent thereon.

In a further development of the invention, the sensor arrangement 19 isadditionally formed by means of an inlet-side third oscillation sensor19 ₃, especially an electrodynamic, third oscillation sensor and/or athird oscillation sensor differential registering oscillations of thefirst measuring tube 18 ₃ relative to the second measuring tube 18 ₄, aswell as an outlet-side fourth oscillation sensor 19 ₄, especially anelectrodynamic, fourth oscillation sensor and/or a fourth oscillationsensor differential registering oscillations of the first measuring tube18 ₃ relative to the second measuring tube 18 ₄. For further improvingsignal quality, as well as also for simplifying the transmitterelectronics 12 receiving the measurement signals, furthermore, the firstand third oscillation sensors 19 ₁, 19 ₃, in the case of electrodynamicoscillation sensors can have their respective cylindrical coilselectrically serially interconnected, for example, in such a manner,that a common oscillation measurement signal represents inlet-sideoscillations of the first measuring tube 18 ₁ relative to the secondmeasuring tube 18 ₂. Alternatively, or in supplementation, also thesecond and fourth oscillation sensors 19 ₂, 19 ₄, in the case ofelectrodynamic oscillation sensors, can have their respectivecylindrical coils electrically serially interconnected in such a manner,that a common oscillation measurement signal of both oscillation sensors19 ₂, 19 ₄ represents outlet-side oscillations of the first measuringtube 18 ₁ relative to the second measuring tube 18 ₂. Additionally, thesensor arrangement is, in such case, so embodied, that each of the 19₁;19 ₂; 19 ₃; 19 ₄, for example, also oscillation sensors equallyconstructed to one another, is, in each case, held on two couplingelements 25 ₃, 25 ₄; 25 ₅, 25 ₆ of first type lying opposite oneanother.

For the aforementioned case, in which the, in given cases, equallyconstructed, oscillation sensors of the sensor arrangement 19 are toregister oscillations of the measuring tubes differential andelectrodynamically, additionally each of the oscillation sensors is, ineach case, formed by means of a permanent magnet held—, for instance, bymeans of one of the mentioned coupling elements of first type—on one ofthe measuring tubes and a cylindrical coil permeated by the magneticfield of the permanent magnet, and held on the, in each case, othermeasuring tube—, for instance, by means of one of the mentioned couplingelements of first type—. In the case of four oscillation sensors 19 ₁;19 ₂; 19 ₃; 19 ₄, these can additionally be arranged in advantageousmanner in the measuring transducer, such that, as directly evident fromthe combination of FIGS. 1, 4, and 6, a minimum distance between thefirst and third oscillation sensors 19 ₁, 19 ₃, or the second and fourthoscillation sensors 19 ₂, 19 ₄ is, in each case, larger than a pipeouter diameter of the first, or second, measuring tube.

It is to be noted here additionally, that although the oscillationsensors of the sensor arrangement 19 illustrated in the example of anembodiment are, in each case, of electrodynamic type, thus, in eachcase, formed by means of a cylindrical magnet coil affixed on one of themeasuring tubes and a therein plunging, permanent magnet affixed on anoppositely lying measuring tube—alternatively or in supplementation—alsoother oscillation sensors known to those skilled in the art, such ase.g. optoelectronic oscillation sensors, can be used for forming thesensor arrangement. Furthermore, as quite usual in the case of measuringtransducers of the type being discussed, supplementally to theoscillation sensors, other, especially auxiliary—, or disturbancevariables registering, sensors can be provided in the measuringtransducer, such as e.g. acceleration sensors, pressure sensors and/ortemperature sensors, by means of which, for example, the ability of themeasuring transducer to function and/or changes of the sensitivity ofthe measuring transducer to the primary measured variable to beregistered, especially the viscosity, the density and, in given cases,also the mass flow rate, as a result of cross sensitivities, or externaldisturbances, can be monitored and, in given cases, correspondinglycompensated.

The exciter mechanism 5 and the sensor arrangement 19 are additionally,as usual in the case of such measuring transducers, particularly alsofor the purpose of transmission the at least one driver signal i_(exc1),or the at least one oscillation measurement signal u_(sens1), coupled insuitable manner, for example, by means of corresponding cableconnections, with the driver circuit Exc, and, respectively, themeasuring—and evaluating circuit μC, both of which are correspondinglyprovided in the transmitter electronics, and these are also connectedwith one another during operation for data communication. The drivercircuit Exc serves, as already mentioned, especially, on the one hand,for producing the driver signal i_(exc1), for example, controlled asregards exciter current and/or exciter voltage, and ultimately drivingthe exciter mechanism 5. On the other hand, the measuring—and evaluatingcircuit μC receives the at least one oscillation measurement signalu_(sens1) of the sensor arrangement 19 and generates therefrom, desired,measured values, thus those representing the viscosity η to be measuredand/or the Reynolds number Re of the flowing medium (X_(η); X_(Re)), oralso such measured values, as a mass flow rate, a totaled mass flowand/or a density rho of the medium to be measured. The so produced,measured values can, in given cases, be visualized onsite, for example,by means of the mentioned display, and operating, element HMI, and/oralso sent to a measuring system superordinated, data processing system,in the form of digital measured data—, in given cases, suitablyencapsulated in corresponding telegrams—and there correspondinglyfurther processed. In an additional embodiment of the measuring systemof the invention, the transmitter electronics is, especially, designedto generate, on the basis of electrical excitation power converted inthe exciter mechanism, especially power dependent on a voltage level andan electrical current level of the first driver signal i_(exc1)—,insofar, of course, also “known” to the transmitter electronics—, thus,that part of said excitation power, which at least partially isconverted into torsional oscillations of the at least two measuringtubes or at least partially into torsion/bending oscillations of the atleast two measuring tubes, a measured value representing the viscosityof the flowing medium and/or a measured value representing the Reynoldsnumber of the flowing medium. For additionally improving the accuracywith which the viscosity, or the Reynolds number is measured by means ofthe measuring system, it is, in supplementation thereto, additionallyprovided, that the transmitter electronics generates the measured valuerepresenting the viscosity of the flowing medium and/or a measured valuerepresenting the Reynolds number of the flowing medium by means of thefirst oscillation signal, especially on the basis of a signal voltageand/or a signal frequency of the first oscillation signal. For the case,in which the exciter mechanism, as mentioned, is operated by means oftwo driver signals i_(exc1), i_(exc2), in given cases, also differentfrom one another as regards signal amplitude and/or phase relationship,fed in at the same time, or the sensor arrangement delivers two or moreoscillatory signals u_(sens1), usens2, representing oscillations of themeasuring tubes, of course, the, insofar, supplementally obtainableinformation concerning the current oscillatory behavior of the tubearrangement, consequently the medium decisively influencing saidoscillatory behavior, correspondingly can be caused to enter into theascertaining of the viscosity, or the Reynolds number, or the additionalmeasured variables to be ascertained.

For the mentioned case, in which the sensor arrangement 19 has fouroscillation sensors, it can be sufficient for the desired accuracy ofmeasurement, to connect together individual oscillation sensors, e.g.pairwise, in order, so, correspondingly to reduce the number of theoscillation measurement signals supplied to the transmitter electronicsand, associated therewith, the extent of circuitry needed for theirprocessing. Equally, also the, in given cases, present, two oscillationexciter can be correspondingly brought together, for example, by aseries connection of the two cylindrical coils, and be correspondinglyoperated by means of a single oscillatory signal. Thus, driver circuitsdirectly known to those skilled in the art, especially driver circuitsutilizing one channel, thus those delivering exactly one driver signalfor the exciter mechanism, can also be used for the operating circuitdriving the exciter mechanism. In case required, however, theoscillation measurement signals delivered by the two or more oscillationsensors can each be preprocessed and correspondingly digitizedindividually in separate measuring channels; equally, in case required,also the, in given cases, present, two or more oscillation exciters canbe operated separately by means of separately produced, or output,driver signals.

The electrical connecting of the measuring transducer to the transmitterelectronics can occur by means of corresponding connecting lines, whichcan be led out of the electronics housing 7 ₂, for example, via cablefeedthrough and directed, at least sectionally, within the transducerhousing. The connecting lines can, in such case, be embodied, at leastpartially, as electrical line wires encased, at least sectionally inelectrical insulation, e.g. in the form of “twisted pair”-lines, flatribbon cables and/or coaxial cables. Alternatively thereto or insupplementation thereof, the connecting lines can, at least sectionallyalso be formed by means of conductive traces of a circuit board,especially a flexible circuit board, in given cases, a lacquered circuitboard; compare, for this, also the initially mentioned U.S. Pat. No.6,711,958 or U.S. Pat. No. 5,349,872. The, for example, also modularlyembodied, transmitter electronics 12 can, as already mentioned, beaccommodated, for example, in a—one part, or, for example, alsomultipart—separate electronics housing 7 ₂, which is arranged removedfrom the measuring transducer or, as shown in FIG. 1, affixed, forforming a single compact device, directly on the measuring transducer 1,for example, externally on the transducer housing 7 ₁. In the case ofthe here illustrated example of an embodiment, consequently, there isplaced on the transducer housing 7 ₁ additionally a neck-like transitionpiece 7 ₃ serving for holding the electronics housing 7 ₂. Within thetransition piece, there can be arranged additionally a feedthrough, forexample, one manufactured by means of glass- and/or plastic pottingcompound, hermetically sealed and/or pressure resistant, for theelectrical connecting lines between measuring transducer 11, thus, thetherein placed oscillation exciters and—sensors, and the mentionedtransmitter electronics 12.

As has already been multiply mentioned, the measuring transducer 11 and,insofar, also the measuring system of the invention are providedparticularly also for measurements at high mass flows of more than 1200t/h in a pipeline of large caliber of 100 mm or more. Taking this intoconsideration, according to an additional embodiment of the invention,the nominal diameter of the measuring transducer 11, which, as alreadymentioned, corresponds to a caliber of the pipeline, in whose course themeasuring transducer 11 to be is used, is so selected, that it amountsto at least 100 mm, especially, however, is greater than 120 mm.Additionally, according to an additional embodiment of the measuringtransducer, it is provided, that each of the measuring tubes 18 ₁, 18 ₂,in each case, has a caliber D₁₈, i.e. a tube inner diameter, amountingto more than 60 mm. Especially, the measuring tubes 18 ₁, 18 ₂ areadditionally so embodied, that each has a caliber D₁₈ of more than 50mm, especially more than 80 mm. Alternatively thereto or insupplementation thereof, the measuring tubes 18 ₁, 18 ₂, according toanother embodiment of the invention, are additionally so dimensioned,that they have, in each case, a measuring tube length L₁₈ of at least800 mm. The measuring tube length L₁₈ corresponds, in the hereillustrated example of an embodiment with equal length measuring tubes18 ₁, 18 ₂, in each case, to a minimum distance between the first flowopening 20 _(1A) of the first flow divider 20 ₁ and the first flowopening 20 _(2A) of the second flow divider 20 ₂. Especially, themeasuring tubes 18 ₁, 18 ₂ are, in such case, so designed, that theirmeasuring tube length L₁₈ is, in each case, greater than 1000 mm.Accordingly, there results at least for the mentioned case, in which themeasuring tubes 18 ₁, 18 ₂, are of steel, in the case of which usuallyused wall thicknesses of over 0.6 mm has a mass of, in each case, atleast 10 kg, especially more than 20 kg. Additionally, it is, however,desirable to keep the empty mass of each of the measuring tubes 18 ₁, 18₂, less than 40 kg.

In consideration of the fact that, as already mentioned, each of themeasuring tubes 18 ₁, 18 ₂, in the case of measuring transducer of theinvention, weighs well over 10 kg, and, in such case, as directlyevident from the above dimensional specifications, can have a capacityof easily 5 l or more, the tube arrangement including the measuringtubes 18 ₁, 18 ₂, at least in the case of medium of high density flowingthrough, can reach a total mass of far beyond 40 kg. Especially in thecase of the application of measuring tubes with comparatively largecaliber D₁₈, large wall thickness and large measuring tube length L₁₈,the mass of the tube arrangement formed of the measuring tubes 18 ₁, 18₂ can be, however, also greater than 50 kg or at least with mediumflowing through, e.g. oil or water, more than 60 kg. As a result ofthis, an empty mass M₁₁ of the measuring transducer, as a whole, amountsalso to far more than 80 kg, and, in the case of nominal diameters D₁₁of essentially greater than 100 mm, even more than 100 kg. As a result,in the case of the measuring transducer of the invention, a mass ratioM₁₁/M₁₈ of an empty mass M₁₁ of the total measuring transducer to anempty mass M₁₈ of the first measuring tube can easily be greater than 5,especially greater than 10.

In order, in the case of the mentioned high empty masses M₁₁ of themeasuring transducer, to use the material applied therefor, as a whole,as optimally as possible and, insofar, to utilize the—most often alsovery expensive—material, as a whole, as efficiently as possible,according to an additional embodiment, the nominal diameter D₁₁ of themeasuring transducer, matched to its empty mass M₁₁, is so dimensioned,that a mass to nominal diameter ratio M₁₁/D₁₁ of the measuringtransducer 11, defined by a ratio of the empty mass M₁₁ of the measuringtransducer 11 to the nominal diameter D₁₁ of the measuring transducer 11is less than 1 kg/mm, especially as much as possible, however, less than0.8 kg/mm. In order to assure a sufficiently high stability of themeasuring transducer 11, the mass to nominal diameter ratio M₁₁/D₁₁ ofthe measuring transducer 11, at least in the case of use of the abovementioned, conventional materials is, however, to choose as much aspossible greater than 0.3 kg/mm. Additionally, according to anadditional embodiment of the invention for additionally improving theefficiency of the installed material, it is provided, that the mentionedmass ratio M₁₁/M₁₈ is kept smaller than 20. For creation of anevertheless as compact as possible measuring transducer of sufficientlyhigh oscillation quality factor and as little as possible pressure drop,according to an additional embodiment of the invention, the measuringtubes, matched to the above mentioned installed length L₁₁ of themeasuring transducer 11, are so dimensioned, that a caliber to installedlength ratio D₁₈/L₁₁ of the measuring transducer, defined by a ratio ofthe caliber D₁₈ at least of the first measuring tube to the installedlength L₁₁ of the measuring transducer 11, amounts to more than 0.02,especially more than 0.05 and/or less than 0.1. Alternatively, or insupplementation, the measuring tubes 18 ₁, 18 ₂, matched to the abovementioned, installed length L₁₁ of the measuring transducer, are sodimensioned, that a measuring tube length to installed length ratioL₁₈/L₁₁ of the measuring transducer, defined by a ratio of the measuringtube length L₁₈ at least of the first measuring tube to the installedlength L₁₁ of the measuring transducer, amounts to more than 0.5,especially more than 0.6 and/or less than 0.95, and/or that anoscillation length to measuring tube length ratio, L_(18x)/L₁₈, of themeasuring transducer, defined by a ratio of the free oscillatory length,L_(18x), of the first measuring tube to the measuring tube length, L₁₈,of the first measuring tube, amounts to more than 0.55, especially morethan 0.6, and/or less than 0.95, especially less than 0.9.

In case required, mechanical stresses and/or vibrations possibly or atleast potentially caused by the vibrating measuring tubes, especiallymeasuring tubes, which are, in the mentioned manner, relatively largedimensioned, at the inlet side or at the outlet side in the transducerhousing, e.g. can be minimized by providing that the measuring tubes 18₁, 18 ₂ are connected mechanically with one another at the inlet andoutlet sides, in each case, by means of coupling elements 24 ₁, 242serving as so-called node plates—in the following referred to ascoupling elements of second type—. Moreover, by means of such couplingelements of second type, be it through their dimensioning and/or theirpositioning on the measuring tubes, mechanical eigenfrequencies of themeasuring tubes and, thus, also mechanical eigenfrequencies of the innerpart formed by means of the tube arrangement as well as thereon placed,additional components of the measuring transducer, such as, forinstance, the oscillation sensors and oscillation exciters, and,insofar, also its oscillatory behavior, as a whole, can, with targeting,be influenced. The coupling elements of second type serving as nodeplates can, for example, be thin plates or washers, especially plates orwashers manufactured of the same material as the measuring tubes, whichare provided with bores corresponding, in each case, with the number andthe outer dimensions of the measuring tubes to be coupled with oneanother, in given cases, supplementally slitted to the edge, so that thewashers are first placed tightly on the respective measuring tubes 18 ₁,or 18 ₂ and, in given cases, thereafter then bonded with the respectivemeasuring tubes, for example, by hard solder or welding. It canadditionally, in the sense of a still simpler and still more exactadjusting of the oscillatory behavior of the measuring transducer, bequite of advantage, when the measuring transducer, as, for example,provided in US-A 2006/0150750, moreover, has still other couplingelements the aforementioned type, for example, thus, as a whole, 4, 6 or8 such coupling elements of second type, serving for forming of inlet-,or outlet-side oscillation nodes for vibrations, especially bendingoscillations, of the first measuring tube and for thereto opposite phasevibrations, especially bending oscillations, of the second measuringtube.

For creation of an as compact as possible measuring transducer ofsufficiently high oscillation quality factor and high sensitivity in thecase of as little as possible pressure drop, according to an additionalembodiment of the invention, the measuring tubes 18 ₁, 18 ₂, matched onthe mentioned free oscillatory length, are so dimensioned, that acaliber to oscillatory length ratio D₁₈/L_(18x) of the measuringtransducer, defined by a ratio of the caliber D₁₈ of the first measuringtube to the free oscillatory length L_(18x) of the first measuring tube,amounts to more than 0.07, especially more than 0.09 and/or less than0.15. Alternatively, or in supplementation, for this, according to anadditional embodiment of the invention, the measuring tubes 18 ₁, 18 ₂,matched to the above mentioned installed length L₁₁ of the measuringtransducer, are so dimensioned, that an oscillation length to installedlength ratio L_(18x)/L₁₁ of the measuring transducer, defined by a ratioof the free oscillatory length L_(18x) of the first measuring tube tothe installed length L₁₁ of the measuring transducer, amounts to morethan 0.55, especially more than 0.6 and/or less than 0.9. According toan additional embodiment of the invention, the oscillation sensors,matched on the free oscillatory length, are so arranged in the measuringtransducer, that a measuring length to oscillatory length ratio of themeasuring transducer, defined by a ratio of the mentioned measuringlength of the measuring transducer to the free oscillatory length of thefirst measuring tube, amounts to more than 0.6, especially more than0.65 and/or less than 0.95. According to an additional embodiment of theinvention, the oscillation sensors, matched to the installed length ofthe measuring transducer, are so arranged in the measuring transducer,that a measuring length to installed length ratio of the measuringtransducer, defined by a ratio of the measuring length to the installedlength of the measuring transducer, amounts to more than 0.3, especiallymore than 0.4 and/or less than 0.7. Alternatively, or insupplementation, the oscillation sensors, in an additional embodiment ofthe invention, matched to the measuring tubes, are so placed in themeasuring transducer, that a caliber to measuring length ratio, D₁₈/L₁₉,of the measuring transducer, defined by a ratio of the caliber D₁₈ ofthe first measuring tube to the measuring length L₁₉ of the measuringtransducer, amounts to more than 0.05, especially more than 0.09. In anadditional embodiment of the invention, the above mentioned, measuringlength L₁₉ is kept less than 1200 mm.

Through the application of two measuring tubes flowed through inparallel, instead of, as previously, a single straight measuring tube,for the registering of measured variables, or of operating parametersserving for diagnosis of the measuring device, such as, for instance,the viscosity, the Reynolds number or an oscillation damping, whichdepend significantly on—, especially, by torsional oscillationsproducible—inner friction forces in the medium, it is, thus, alsopossible to manufacture, cost effectively, measuring transducers of thedescribed type also in the case of large mass flow rates, or with largenominal diameters of far over 100 mm, on the one hand, with a highaccuracy of measurement coupled with an acceptable pressure drop,especially of, for instance, 1 bar or less, and, on the other hand, tokeep the installed mass, as well as also the empty mass, of suchmeasuring transducers sufficiently in limits, that, in spite of largenominal diameter, the manufacture, transport, installation, as well asalso operation can always still occur economically sensibly. Especiallyalso by implementing previously explained measures further developingthe invention—individually or also in combination—measuring transducersof the type being discussed can also in the case of large nominaldiameter be so embodied and so dimensioned, that a mass ratio of themeasuring transducer defined by a ratio of the mentioned empty mass ofthe measuring transducer to a total mass of the tube arrangement (formedby means of the measuring tubes) as well as all thereto held, additionalcomponents of the measuring transducer influencing the oscillatorybehavior of the tube arrangement can be kept less than 3, especiallyless than 2.5.

The invention claimed is:
 1. A method for determining the viscosity of amedium with a Coriolis mass flowmeter having at least two measuringtubes through which a medium can flow and a measuring device having atleast two actuator assemblies, the actuator assemblies being arranged onboth sides of a measuring tube plane defined by a central axis of themeasuring tubes and outside of the measuring tube plane, said methodcomprising: exciting the measuring tubes with the measuring device to anoppositely directed torsional oscillation with the actuator assembliesbeing alternately actuated in opposing effective directions anddetermining at least the viscosity of the medium by evaluation ofmeasured values obtained from the measuring device, said measured valuescomprising the amplitude of torsional oscillation are reached.
 2. Themethod according to claim 1, wherein both measuring tubes are excited atthe same time by the measuring device to excitation at torsionaloscillation with a frequency F₁, and additionally, at plane oscillationin the common measuring tube plane with a frequency F₂ that differs fromfrequency F₁.
 3. The method according to claim 2, wherein a differenceof at least 2% of the frequency of the torsional oscillation existsbetween the frequency F₁ of the torsional oscillation and the frequencyF₂ of the plane oscillation.
 4. The method according to claim 1, whereinthe measuring tubes are excited by the measuring device to torsionaloscillation with a frequency F₁ and at different times to planeoscillation with a frequency F₂ that differs from frequency F₁.
 5. Themethod according to claim 4, wherein a difference of at least 2% of thefrequency of the torsional oscillation exists between the frequency F₁of the torsional oscillation and the frequency F₂ of the planeoscillation.
 6. The method according to claim 1, wherein a dampingfactor of the torsional oscillation of both measuring tubes isdetermined from the measured values of the measuring device, and whereinthe viscosity of the medium is calculated using the damping factor. 7.The method according to claim 1, wherein the measuring device includesat least four sensor assemblies, wherein two sensor assemblies arearranged above and below the measuring tube plane and wherein thetorsional oscillation is detected with both sensor assemblies located onone side of the measuring tube plane and the plane oscillation isdetected with both sensor assemblies located on the other side of themeasuring tube plane.
 8. The method according to claim 1, whereindiagnostic information about the maintenance status of the Coriolis massflowmeter is derived from the measured values of the torsionaloscillation.
 9. The method according to claim 1, wherein the actuatorassemblies are used as a sensor assemblies for determining measuredvalues after exciting the measuring tube to at least one of torsionaloscillation and plane oscillation.
 10. The method according to claim 1,wherein the measured values are also used to determine the mass flow ofa medium flowing in the measuring tubes.
 11. A method for determiningthe viscosity of a medium by means of a measuring transducer including:first and second measuring tubes for conveying flowing medium, anexciter mechanism adapted to cause each of the measuring tubes toexecute mechanical oscillations and a sensor arrangement adapted toregister mechanical oscillations of the at least two measuring tubes,said method comprising: flowing medium through said measuring tubes;feeding electrical power into said exciter mechanism to excite saidmeasuring tubes to torsional oscillations; using said sensor arrangementto produce at least one oscillation measurement signal, which representsat least partially torsional oscillations of at least one of saidmeasuring tubes; and determining the viscosity of the medium on basis ofelectrical excitation power converted in said exciter mechanism forexciting said measuring tubes and on basis of said at least oneoscillation measurement signal.
 12. The method as claimed in claim 11,further comprising: converting said electrical excitation power fed intosaid exciter mechanism at least partially, into torsional oscillationsof the first measuring tube and into torsional oscillations of thesecond measuring tube, which are opposite and equal to the torsionaloscillations of the first measuring tube.